TerminalFix: PNG Steganography, (Mon, Sep 21st)

ANALYST: BIVASH KUMAR NAYAK (CHIEF SECURITY ARCHITECT) • PUBLISHED: Monday, 21 September 2026
CYBERDUDEBIVASH® INTEL FACTORYSENTINEL APEX™ // ADVANCED CTI DOSSIER
TerminalFix: PNG Steganography, (Mon, Sep 21st)
CYBERDUDEBIVASHCDB-CTI-2026-7852E2311F19
SEVERITYUNSPECIFIED
CONFIDENCEMEDIUM
TLPTLP:CLEAR
SOURCESANS Internet Storm Center
GENERATED UTC2026-09-21T14:15:15.885805Z
CERTIFICATIONPublic Intelligence Certification: SOURCE_ONLY_PRELIMINARY (automated evidence-graph certification — see Provenance for the source basis)
EVIDENCE-PRESERVING PRESENTATIONSOURCE-LINKEDREPORTX BOUNDARIES RETAINED
PROMPT / REASONING LEAKAGEBLOCKED BY V8DUPLICATE CANONICAL SECTIONSBLOCKED BY V8SOURCE / PROVENANCERETAINEDATT&CK STATENOT ESTABLISHEDIOC STATENOT ESTABLISHEDEXPOSURE CLAIMINTERNAL TELEMETRY REQUIRED
INTELLIGENCE CONFIDENCE // EVIDENCE MATRIXNON-PROBABILISTIC
ANALYTIC CONFIDENCEMEDIUM
SOURCE BASISSANS Internet Storm Center
CORROBORATIONSINGLE SOURCE
TECHNICAL SPECIFICITYEVIDENCE PRESENT
OBSERVABLE COVERAGENOT ESTABLISHED
INTERNAL OBSERVABILITYREQUIRES CUSTOMER TELEMETRY

States reflect the rendered evidence product. They are not statistical probabilities and do not establish customer-specific exposure.

ENTERPRISE EXPOSURE DECISION ENGINEZERO-ASSUMPTION
EXPLOITATIONNot applicable to this intelligence format
REMEDIATIONNot applicable to this intelligence format
ATT&CKNOT ESTABLISHED
OBSERVABLESNOT ESTABLISHED
DETECTIONGUIDANCE_ONLY
CUSTOMER EXPOSUREREQUIRES INTERNAL VALIDATION
CUSTOMER COMPROMISENOT ESTABLISHED BY PUBLIC INTELLIGENCE
ESCALATIONTELEMETRY-CONDITIONED
INTELLIGENCEEXPOSURE VALIDATEDSUSPICIOUS ACTIVITYCONFIRMED INCIDENT
ATTACK SURFACE // CONTROL PATHANALYTICAL MODEL
01SOURCE SIGNAL02EVIDENCE VALIDATION03ENTERPRISE RELEVANCE04SECURITY TELEMETRY05SOC DECISION

This control path organizes validation and telemetry decisions. It is not a claim that every stage occurred in the reported event.

INTELLIGENCE TIMELINE // CHRONOLOGYSOURCE-LINKED
01

The normalized source publication timestamp is 2026-09-21T10:33:53+00:00.

02

Additional intrusion, exploitation, disclosure, or remediation timestamps are not asserted unless they are present in the cited evidence body below.

SOC / IR DECISION LIFECYCLE
GOVERNIDENTIFYPROTECTDETECTRESPONDRECOVER
Framework-oriented navigation only; not a compliance or attestation statement.
SOURCE CONFIDENCE & CORROBORATIONQUALITATIVE · NOT PROBABILITY
SOURCE RELIABILITYC
INFORMATION CREDIBILITY3 — Possibly True
CORROBORATIONSINGLE SOURCE
ANALYTIC CONFIDENCEMEDIUM
EVIDENCE GRAPH // CLAIM TRACEABILITYNO SYNTHETIC NODES
SOURCESANS Internet Storm Center
C-001Source publisher: SANS Internet Storm Center
C-002Source published: 2026-09-21T10:33:53+00:00
REPORTXCDB-CTI-2026-7852E2311F19
DECISION LAYERSOC VALIDATION
ENTERPRISE EXPOSURE VALIDATION CHECKLISTSTATUS · NOT ASSESSED
Validation aid only — not a customer risk score. Exposure is confirmed only by internal inventory/telemetry or separately corroborated evidence.
  1. Does the cited technology, service, identity, dependency, sector, or behavior exist in the environment?
  2. Is internal telemetry available to confirm or reject enterprise relevance?
  3. Are operational pivots limited to source-backed observables and behaviors?
  4. Is public-source reporting being kept separate from confirmed customer impact?
  5. Is the validation decision timestamped and evidence-preserved for later re-evaluation?
INTELLIGENCE CHRONOLOGY & PROVENANCE RAILSOURCE → PUBLICATION
01SOURCE PUBLISHED2026-09-21T10:33:53+00:00
02EVIDENCE NORMALIZEDREPORTCONTEXT + REPORTX
03SOURCE RECORD SEALED7852e2311f195b65…
04DOSSIER GENERATED2026-09-21T14:15:15.885805Z
05PUBLICATION CONTROLFAIL-CLOSED INTEGRITY GATE
EXECUTIVE DECISION SUPPORTCANONICAL REPORTX SOURCE
D-01

No internal exposure evidence: retain as intelligence, document the negative exposure basis, and continue collection.

D-02

Exposure confirmed but compromise unconfirmed: prioritize supported remediation and heightened telemetry while avoiding unsupported incident claims.

D-03

Internal malicious activity confirmed: activate the organization's incident-response process using the preserved evidence and scoped telemetry.

INTELLIGENCE GAP & COLLECTION TRACKER3 OPEN
GAP-001Customer-specific exposure is not established by the public source record.OPEN
GAP-002Customer-specific compromise or impact is not established unless internal telemetry is supplied.OPEN
GAP-003Any source dimension not represented in the normalized evidence graph requires additional authoritative collection before it can drive a material claim.OPEN
INTELLIGENCE OUTPUTS API DOCUMENTATION STIX 2.1 · ENTERPRISE IOC API PUBLIC DOSSIER · SOURCE-LINKED
PUBLIC INTELLIGENCE INTEGRITY // Severity, corroboration, artifact availability, technical evidence class, information-sharing label, and paid delivery links are canonicalized from the rendered evidence product. Source-only evidence is labeled preliminary.
ASTRA REVENUE INTELLIGENCE // PRODUCT ACCESSPUBLIC DOSSIER → OPERATIONAL INTELLIGENCE
This public dossier remains source-linked intelligence. Customer exposure or compromise is never inferred here. Paid tiers add authenticated operational delivery, not stronger factual certainty.
DIRECT CHECKOUT // Canonical plan pricing is loaded from the billing API. Razorpay instant checkout is offered where available; verified UPI/bank fallback remains available. Paid access changes delivery and entitlement, never intelligence certainty.
PUBLICPUBLIC DOSSIER

Source-linked analysis, provenance, evidence boundaries, executive and SOC decision support.

API DOCUMENTATION
IOC + detection + higher-rate operational intelligenceSTART SOC PRO CHECKOUT →
PROMPT LEAKAGE PASS CANONICAL UNIQUENESS PASS EVIDENCE BOUNDARY ENFORCED SOURCE PROVENANCE RETAINED
SOC OPERATIONS CONTROL PLANE // CTI EVIDENCE GRAPHV8
REPORT FAMILYCyber Threat Intelligence
EXPLOITATION STATENot applicable to this intelligence format
REMEDIATION STATENot applicable to this intelligence format
EVIDENCE TIERSOURCE_ONLY_PRELIMINARY
ANALYTICAL FOCUSEVIDENCEEXPOSURESOC ACTION
ATT&CKNOT ESTABLISHED
OBSERVABLESNOT ESTABLISHED
DETECTIONGUIDANCE_ONLY
HUNTINGGUIDANCE_ONLY
SOC PLAYBOOKGENERIC_VALIDATION_PLAYBOOK
CONFIDENCEMEDIUM
01SANS Internet Storm Center02EVIDENCE GRAPH03REPORTX04SOC DECISION SUPPORT
SOC ANALYST 60-SECOND BRIEFEVIDENCE-BOUNDED
01

WHAT HAPPENED

TerminalFix: PNG Steganography, (Mon, Sep 21st). Source-linked Cyber Threat Intelligence with evidence-bounded analysis, exposure validation, SOC decision support, and retained provenance. Source-backed iocs, att&ck mappings or executable detection artifacts are not established in this record.

02

WHAT SOC SHOULD DO

Validate whether the affected technology, identity, dependency, service, or victim context exists internally. Preserve relevant logs and timestamps before destructive containment when an internal match is found. Escalate from intelligence validation to incident response only when internal telemetry or independently cited evidence supports the transition.

03

EVIDENCE BOUNDARY

Confidence is bounded by source reliability, information credibility, corroboration state, and unresolved contradictions already computed by ReportX. Structural compilation never raises epistemic confidence.

EVIDENCE LEDGER SNAPSHOT2 CLAIMS
CLAIMEVIDENCE-BOUND STATEMENTSTATE
C-001Source publisher: SANS Internet Storm CenterSOURCE-LINKED
C-002Source published: 2026-09-21T10:33:53+00:00SOURCE-LINKED
TerminalFix: PNG Steganography, (Mon, Sep 21st)
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📅 September 21, 2026  |  📂 Malware Research  |  🛡 CYBERDUDEBIVASH®

Executive Summary

TerminalFix: PNG Steganography, (Mon, Sep 21st). Source-linked Cyber Threat Intelligence with evidence-bounded analysis, exposure validation, SOC decision support, and retained provenance. Source-backed iocs, att&ck mappings or executable detection artifacts are not established in this record.

Key Judgements

Key Judgements are derived from validated ReportX claim identifiers rather than a second free-form model request. They may prioritize validation and collection, but they do not convert source-reported claims into confirmed customer impact.

Verified Facts

  • Source publisher: SANS Internet Storm Center
  • Source published: 2026-09-21T10:33:53+00:00

Threat Classification

Report family: Cyber Threat Intelligence. Exploitation state: Not applicable to this intelligence format. Remediation state: Not applicable to this intelligence format. These labels come from the normalized report context and remain bounded by cited evidence.

Threat Severity Assessment

Severity is interpreted from structured scoring or source evidence when present. No customer-specific risk score, blast radius, or compromise state is inferred by this compiler.

Evidence & Source Assessment

Primary provenance is SANS Internet Storm Center. The compiler distinguishes source-reported material from independently structured NVD/CISA/EPSS evidence when those fields are actually present.

Timeline & Chronology

The normalized source publication timestamp is 2026-09-21T10:33:53+00:00. Additional intrusion, exploitation, disclosure, or remediation timestamps are not asserted unless they are present in the cited evidence body below.

Business Impact

Customer-specific business impact is not established by a public source record alone. Decision value comes from determining whether relevant assets, identities, dependencies, or services are actually present and exposed.

Enterprise Exposure Assessment

  • Inventory and ownership teams should determine whether the technology or service named in the cited record exists in the environment before assigning incident status.
  • A positive exposure determination requires asset, version, identity, dependency, cloud/SaaS, or equivalent internal telemetry that can be tied to the cited condition.
  • A negative determination should record the inventory evidence and timestamp used so the decision can be revalidated if the source record changes.

Technical Analysis

EVIDENCE CLASS // GENERAL VULNERABILITY-CLASS CONTEXT. The displayed evidence ledger does not establish CVE-specific exploit mechanics beyond its source-linked claims. Treat prerequisites, parser path, memory-corruption consequences, execution potential, and mitigation behavior as unresolved for this CVE until authoritative upstream evidence is collected.
CYBER THREAT INTELLIGENCE · UNRATED
CDB-CTI-2026-7852E2311F19 · Generated 2026-09-21T14:15:15.870350Z
Executive Summary

Microsoft Security Research published an interesting blog post " TerminalFix campaign deploys a reverse tunnel through multistage intrusion " about a malware campaign. The aspect that I want to take a closer look at, is the fact that the threat actors used PNG files with steganography. I reached out to the researchers and they kindly shared the IOCs for the PNG files with me.

Decision: Validate relevance and exposure using the cited source and internal evidence before treating this record as an incident, confirmed compromise, or customer-specific finding.

Threat Classification and Evidence Status
Intelligence family
Cyber Threat Intelligence
Technical severity
UNRATED
Exploitation
Not applicable to this intelligence format
Patch/remediation
Not applicable to this intelligence format
Verified Facts
Source type: Cyber Threat Intelligence
Source publication time: 2026-09-21T10:33:53+00:00
KEV catalog check: Unknown or unavailable; no negative claim is made.
Intelligence Assessment

Evidence boundary: Conclusions are limited to the cited source record. No affected-customer scope, attribution, exploitation, or financial impact is inferred.

Operational Decisions
Validate relevance: Determine whether the cited technology, organization, actor, or behavior exists in the environment.
Collect evidence: Preserve source records and internal telemetry before escalating a hypothesis to an incident or vulnerability finding.
Assign ownership: Route confirmed exposure to the accountable security, engineering, risk, or privacy owner with an explicit decision deadline.
Source Evidence Extract
Source Publisher: SANS Internet Storm Center
Original Article: https://isc.sans.edu/diary/rss/33318
Feed Evidence Type: content:encoded
Microsoft Security Research published an interesting blog post "
TerminalFix campaign deploys a reverse tunnel through multistage intrusion
" about a malware campaign. The aspect that I want to take a closer look at, is the fact that the threat actors used PNG files with steganography. I reached out to the researchers and they kindly shared the IOCs for the PNG files with me.
The first image is a small PNG file (
f5f1eb6d43dd61d5b069c250e5c666384f7417d0c95014773bf9edf8ff13bebe
).
Analysis with
pngdump.py
reveals that this is a proper PNG file:
There is no data appended to the end of the image. The image starts with the expected header, and has the 3 type of chunks one expects to find in a minimal PNG file: IHDR, IDAT and IEND. There is no metadata that can contain a payload. The IDAT chunk contains the pixels of the image: encoded and ZLIB compressed. The fact that pngdump was able to decompress the IDAT data, is another indication that this is a PNG image with valid IDAT data. It consists of 111 lines and 112 columns. All of the filters of the scanlines are known filters: yet another indication that this is valid data. Thus everything indicates that this is a valid image. If it contains a payload, then it hides in the pixels, and we can confirm that steganography is used.
Let's take a look at the decompressed IDAT data (the scanlines that make up the image):
We can see strings like MZ, .text, .data, ... All strings often found inside a Windows executable (PE file). It's very likely that there is a PE file hiding in the pixel data, but what we see here is the encoded pixel data.
The picture consists of 111 scanlines. The first byte is the type of the filter. Value 01, seen at the start of the decompressed data, indicates that the first line is encoded with the SUB (subtract) filter. 8 bits are used to encode pixel data, and the colortype is 6, e.g., RGBA. This means that there are 4 bytes for each pixel: 1 for Red, 1 for Green, 1 for Blue and 1 for Alpha (transparency). 112 columns times 4 bytes gives 448 bytes per scanline.
A filter of type SUB means that the RGBA values of a pixel are substracted from the RGBA values of the previous pixel (except for the first pixel). Thus this is a transformation that needs to be applied to obtain the raw pixel data. And SUB is not the only filter, there are 5 different filter types.
But the easiest way to obtain the raw bitmat data is to use option -R (--raw):

This extract is escaped and rendered from the ingested source record; generated analysis is not presented as a source fact.

Detection Engineering
DETECTION STATUS: NOT_APPLICABLE

The source is an intelligence/news record without threat-specific telemetry or observables.

Track the cited development through the relevant risk, governance, or incident-management process.
Create detection content only after a concrete attack behavior, log source, and testable observable are confirmed.
References
AI-Native Automated Intelligence — Evidence-Graph Verified. Public reference draft — not a certified customer deliverable. Customer-specific action requires exposure validation and accountable human approval.
Source Reliability & Corroboration

SANS Internet Storm Center

Source Reliability: C
Information Credibility: 3 (Possibly True)
Overall Analytical Confidence: MEDIUM

Reported by a single identified source; an independent second source has not been found (see the evidence ledger).

Structured ATT&CK Assessment

T1071 — Application Layer Protocol (command-and-control)

STATUS: CONDITIONAL · CONFIDENCE: MEDIUM

Source text evidence: "t image is a small PNG file ( f5f1eb6d43dd61d5b069c250e5c666384f7417d0c95014773bf9edf8ff13bebe ). Anal"

Limitation: Derived from source-text phrase matching, not independently confirmed or observed in any environment.

Intelligence Gaps
Known Unknown: Whether an independent second source corroborates this record has not been assessed.
Would be resolved by: A second, independent source reporting the same underlying fact.
Indicators / Observables
Domain: blog[.]didierstevens[.]com
SHA-256: f5f1eb6d43dd61d5b069c250e5c666384f7417d0c95014773bf9edf8ff13bebe
Indicators are defanged for safe display (e.g. hxxp:// / [.]) -- refang before use in blocking or detection tooling.

Report-Type Deep Dive

This Cyber Threat Intelligence record is analyzed according to the evidence available for its family. Unsupported exploit chains, malware capabilities, breach scope, attribution, encryption, exfiltration, and regulatory consequences are intentionally not synthesized.

MITRE ATT&CK Assessment

Not established in cited evidence. ATT&CK technique mapping requires source-backed behavior. Any mappings present in the preserved analytical body are subject to the existing ReportX semantic gate; the compiler adds none of its own. The factory does not infer the missing fact from absence of evidence.

Indicators & Observables

VERIFIED ARTIFACTS AVAILABLE. Indicators extracted directly from the sourced article are published below in the Indicators / Observables section (defanged for safe display).

Detection Engineering Guidance

Detection content remains evidence-conditioned. Production rules require source-backed behavior plus the telemetry needed to validate precision; otherwise the correct output is a telemetry specification rather than fabricated executable logic.

Detection Validation & Required Telemetry

  • Identify the telemetry source and fields needed to observe the cited behavior before promoting detection logic.
  • Replay or safely simulate only evidence-supported behavior, measure expected false positives, and retain test evidence with the rule version.
  • Do not represent syntax validation as production efficacy; deployment requires environment-specific validation and accountable approval.

Threat Hunting Queries

Threat hunting should begin with exposure to the technology or service named in the cited record and then pivot only on observables or behavior established in cited evidence. Absence of a source-backed pivot is an intelligence gap, not permission to invent one.

SOC Analyst Playbook

  • Validate whether the affected technology, identity, dependency, service, or victim context exists internally.
  • Preserve relevant logs and timestamps before destructive containment when an internal match is found.
  • Escalate from intelligence validation to incident response only when internal telemetry or independently cited evidence supports the transition.

Incident Response & Containment Decision Plan

Public threat intelligence alone does not establish an internal incident. If internal evidence confirms relevance, preserve evidence, scope affected assets and identities, contain the validated path, eradicate the supported cause, recover, and verify recurrence controls.

Remediation & Validation Plan

  • Remediation state from the normalized record: Not applicable to this intelligence format.
  • Apply vendor/CISA remediation only when that action is actually present in trusted evidence; otherwise obtain the authoritative remediation source before changing production systems.
  • After change, verify asset/version state, exposure path, relevant telemetry, and rollback readiness rather than assuming the change succeeded.

Executive Decision Matrix

  • No internal exposure evidence: retain as intelligence, document the negative exposure basis, and continue collection.
  • Exposure confirmed but compromise unconfirmed: prioritize supported remediation and heightened telemetry while avoiding unsupported incident claims.
  • Internal malicious activity confirmed: activate the organization's incident-response process using the preserved evidence and scoped telemetry.

Executive Recommendations

  • Validate enterprise relevance to the technology or service named in the cited record before treating the public record as a customer-specific finding.
  • Prioritize evidence-backed remediation, telemetry coverage, and verification over severity labels alone.
  • Keep unresolved exploitation, attribution, breach scope, and impact statements explicitly unresolved until corroborating evidence exists.

Intelligence Gaps & Collection Requirements

  • Customer-specific exposure is not established by the public source record.
  • Customer-specific compromise or impact is not established unless internal telemetry is supplied.
  • Any source dimension not represented in the normalized evidence graph requires additional authoritative collection before it can drive a material claim.

Analytic Confidence & Limitations

Confidence is bounded by source reliability, information credibility, corroboration state, and unresolved contradictions already computed by ReportX. Structural compilation never raises epistemic confidence.

Forecast & Outlook

No new future event is predicted by the compiler. Forecast statements, when present in the preserved analytical body, must remain tied to ReportX supporting observation claims and explicit confidence rationale.

References

🎯 Recommended For This Threat

Incident ResponseDigital Forensics · IR Retainer
Detection EngineeringVersioned Sigma · YARA · SIEM Content

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Contact: bivash@cyberdudebivash.com · Website: https://cyberdudebivash.com
Intelligence source: https://isc.sans.edu/diary/rss/33318 · CYBERDUDEBIVASH® SENTINEL APEX Evidence Engine v3.0
Provenance and Certification
Report IDCDB-CTI-2026-7852E2311F19
Source systemglobal_rss
Source published2026-09-21T10:33:53+00:00
Source-record SHA-2567852e2311f195b65fdb517cac62a75d52ae7a36eef7ef560bf17a038990f5513
Generated UTC2026-09-21T14:15:15.885805Z
Production ModeAI-Native Automated Intelligence — Evidence-Graph Verified
CertificationPublic Intelligence Certification: SOURCE_ONLY_PRELIMINARY (automated evidence-graph certification — see Provenance for the source basis)