CVE-2026-77775 — CVSS 8.6 HIGH Severity | NVD Vulnerability Record

ANALYST: BIVASH KUMAR NAYAK (CHIEF SECURITY ARCHITECT) • PUBLISHED: Saturday, 22 August 2026
CVE-2026-77775 — CVSS 8.6 HIGH Severity | NVD Vulnerability Record
■ Executive Risk Command Center
CVE ID
CVE-2026-77775
CVSS Score
8.6
HIGH
CISA KEV
Not Listed
Not present in the verified catalog snapshot; this does not prove absence of exploitation

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🔍 CVE-2026-77775  |  ⚠ CVSS 8.6  |  📅 August 22, 2026  |  📂 Vulnerabilities  |  🛡 CYBERDUDEBIVASH®
CVE VULNERABILITY ADVISORY · HIGH
CDB-CTI-2026-48FA5841A0A5 · Generated 2026-08-22T04:50:36.702039Z
Executive Summary

Headroom's LLM proxy lets a client choose the upstream destination with the x-headroom-base-url request header. _resolve_openai_upstream_base in headroom/proxy/handlers/openai.py accepts the header value, requires only that it parse with an http or https scheme and a hostname, and returns it for use as the upstream base; _select_passthrough_base_url in headroom/providers/proxy_routes.py reads the same header for the passthrough routes. No check rejects loopback, link-local, or RFC 1918 destinations, and because the component is a proxy the upstream response is returned to the caller, so the request reaches internal services and cloud metadata addresses and their responses are disclosed. The Authorization header accompanying the request is forwarded unchanged to the caller-designated host. The pip console script binds 127.0.0.1 by default, but the reference docker-compose.yml ships --host 0.0.0.0 with published ports and no required HEADROOM_PROXY_TOKEN, which the server itself warns about at startup, so a deployment following the shipped compose exposes the affected data-plane routes to the network without authentication. CVSS Score: 8.6 CWE: CWE-918

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
CVE Vulnerability Advisory
Technical severity
HIGH
Exploitation
Not confirmed by available evidence; not in verified KEV snapshot
Patch/remediation
Availability not established in the source record — verify vendor guidance
Verified Facts
Source type: CVE Vulnerability Advisory
Source publication time: 2026-08-21T12:16:36.813000
CVE: CVE-2026-77775
CVSS base score: 8.6
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
CWE: CWE-918
KEV catalog check: Not present in the successfully retrieved catalog snapshot; this does not prove absence of exploitation.
Technical Analysis

Vulnerability class: Server Side Request Forgery. Assessment: Active exploitation is not confirmed by the available evidence. This vulnerability is exploitable over the network, requiring no privileges and no user interaction. Prioritization must combine technical severity, exposure, asset criticality, and compensating controls.

Exposure and Remediation Decisions
P0 — Inventory: Confirm the affected product and version against authoritative vendor/NVD data; prioritize internet-facing and business-critical assets.
P0 — Remediation: Availability not established in the source record — verify vendor guidance
P1 — Compensating controls: Restrict exposure, enforce least privilege, and apply vendor-supported mitigations when immediate remediation is not possible.
P1 — Retrospective review: Search only the telemetry relevant to the affected component and validated vulnerability class; absence of alerts does not prove absence of exploitation.
Source Evidence Extract
CVE ID: CVE-2026-77775
Description: Headroom's LLM proxy lets a client choose the upstream destination with the x-headroom-base-url request header. _resolve_openai_upstream_base in headroom/proxy/handlers/openai.py accepts the header value, requires only that it parse with an http or https scheme and a hostname, and returns it for use as the upstream base; _select_passthrough_base_url in headroom/providers/proxy_routes.py reads the same header for the passthrough routes. No check rejects loopback, link-local, or RFC 1918 destinations, and because the component is a proxy the upstream response is returned to the caller, so the request reaches internal services and cloud metadata addresses and their responses are disclosed. The Authorization header accompanying the request is forwarded unchanged to the caller-designated host. The pip console script binds 127.0.0.1 by default, but the reference docker-compose.yml ships --host 0.0.0.0 with published ports and no required HEADROOM_PROXY_TOKEN, which the server itself warns about at startup, so a deployment following the shipped compose exposes the affected data-plane routes to the network without authentication.
CVSS Score: 8.6
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
CWEs: CWE-918

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

MITRE ATT&CK Mapping
Initial Access → Exploit Public-Facing Application (T1190), conditional on an exposed web application.
Mappings are conditional analytical aids, not claims that the technique occurred. Promote a mapping to observed only after telemetry confirms the behavior.
Detection Engineering
DETECTION STATUS: SYNTAX_VALIDATED_EXPERIMENTAL

The source identifies a request-oriented vulnerability class with testable class-level request indicators.

Collect decoded request target, destination/upstream address, response status, and application error telemetry.
Treat matches as investigation leads; confirm product route and affected version before escalation.
SIGMA YAML — SYNTAX VALIDATED · EXPERIMENTAL · ENVIRONMENT TUNING REQUIRED
title: Potential Server Side Request Forgery Probing Related to CVE-2026-77775
id: b8e7e6ad-0667-5f80-849c-3df971d729d4
status: experimental
description: Detects class-level request indicators. It does not establish successful exploitation.
references:
- https://nvd.nist.gov/vuln/detail/CVE-2026-77775
author: CYBERDUDEBIVASH Sentinel APEX Detection Engineering
date: '2026-08-22'
logsource:
  category: webserver
detection:
  selection:
    cs-uri-query|contains:
    - 169.254.169.254
    - 127.0.0.1
    - localhost
  condition: selection
falsepositives:
- Security testing
- Legitimate encoded application parameters
level: medium
tags:
- attack.initial-access
- attack.t1190
SENTINEL KQL — SYNTAX VALIDATED · EXPERIMENTAL · ENVIRONMENT TUNING REQUIRED
// Potential Server Side Request Forgery Probing Related to CVE-2026-77775
// report: CDB-CTI-2026-48FA5841A0A5
// Placeholder table name -- bind to your ingested web/WAF request-log table (e.g. AzureDiagnostics with Category == 'ApplicationGatewayAccessLog', W3CIISLog, or a custom table) and confirm the request-URI column name before deployment.
WebRequestLogs
| where RequestUri has_any ("169.254.169.254", "127.0.0.1", "localhost")
| project TimeGenerated, RequestUri, ClientIP
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.
Role-Based Decisions
Vulnerability Manager: Track against cve vulnerability advisory intake. Exploitation status: Not confirmed by available evidence; not in verified KEV snapshot. Patch status: Availability not established in the source record — verify vendor guidance. — Prioritization reflects this record's own exploitation/patch evidence, not a fixed severity template.
Limitations: Reflects only this record's own reported exploitation and patch status; does not confirm whether the affected component is deployed in any specific environment.
SOC Manager: Review the detection guidance below before enabling any blocking action on it. — Detection maturity for this record is stated explicitly, not assumed production-ready.
Limitations: Detection guidance is evidence-scoped to this record; does not confirm the described technique has been observed in any specific environment.
Source Reliability & Corroboration

nvd

Source Reliability: B
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).

Threat Hunting — hunt-CDB-CTI-2026-48FA5841A0A5-exposure

Hypothesis: If CVE-2026-77775 is deployed and reachable as described by CDB-CTI-2026-48FA5841A0A5's evidence (CVE: CVE-2026-77775), telemetry consistent with the vulnerability class below may show attempted or successful exploitation.

Required telemetry: Collect decoded request target, destination/upstream address, response status, and application error telemetry.
Required telemetry: Treat matches as investigation leads; confirm product route and affected version before escalation.
Pivot: Pivot on the affected component's inventoried version/build identifier, where available.
Pivot: Pivot on network paths and identities with reachability to the affected component.
Expected if true: Requests, processes, or events consistent with the vulnerability class described in this report's Technical Analysis, occurring after the CVE's public disclosure date and targeting the specific affected component.
Negative indicator: No matching telemetry for the affected component across the retrospective lookback window.
Negative indicator: The affected component is confirmed not deployed, or not reachable as this CVE describes.
False-positive risk: Legitimate administrative, diagnostic, or scanning activity against the same component can resemble exploitation attempts; corroborate with authentication context and known-good change records before escalating.

Success criteria: A specific, timestamped, corroborated telemetry match consistent with the vulnerability class, tied to the confirmed affected component.

Escalation criteria: Escalate to incident response only when a validated telemetry match is corroborated by at least one additional independent signal (e.g. an authentication anomaly or unexpected process lineage) -- a single matching log line alone is not sufficient grounds for escalation.

Confidence: MEDIUM — Maturity: PROPOSED (not independently confirmed by execution against real telemetry)

Limitations: Derived from the vulnerability class alone; does not confirm the affected component is actually deployed in the reader's environment, nor that matching telemetry represents genuine exploitation rather than benign activity.

Structured ATT&CK Assessment

T1190 — Exploit Public-Facing Application (initial-access)

STATUS: CONDITIONAL · CONFIDENCE: MEDIUM

Initial Access → Exploit Public-Facing Application (T1190), conditional on an exposed web application.

Limitation: Conditional on the deployment/exploitation scenario described in the source record; not confirmed by telemetry.

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
CVE: CVE-2026-77775
Indicators are defanged for safe display (e.g. hxxp:// / [.]) -- refang before use in blocking or detection tooling.

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Contact: bivash@cyberdudebivash.com · Website: https://cyberdudebivash.com
Intelligence source: https://nvd.nist.gov/vuln/detail/CVE-2026-77775 · CYBERDUDEBIVASH® SENTINEL APEX Evidence Engine v3.0
Provenance and Certification
Report IDCDB-CTI-2026-48FA5841A0A5
Source systemnvd
Source published2026-08-21T12:16:36.813000
Source-record SHA-25648fa5841a0a557b3cffe404f438d630123491eb24070c83db157f98fe6958595
Generated UTC2026-08-22T04:50:36.778627Z
Production ModeAI-Native Automated Intelligence — Evidence-Graph Verified
CertificationPublic Intelligence Certification: FLASH_READY (automated evidence-graph certification — see Provenance for the source basis)