CVE-2026-73431: CIRCL Vulnerability-Lookup Stateless Token Replay Account Takeover

HERMES

HERMES THREAT SCORE & OPERATIONAL EXPLOITABILITY

Target: CIRCL Vulnerability-Lookup (vulnerability-lookup <= 5.5.1)

Confidence: 96%

82 / 100

HIGH

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 19 / 20

Threat Activity 14 / 20

Weaponization 16 / 20

Exposure 17 / 20

Prevalence 14 / 20

Impact 18 / 20

Exploit Maturity 16 / 20

Attack Chain Potential 17 / 20

⚖️ Divergence & Operational Rationale

Both CVSS v3.1 (8.8 High) and Hermes Threat Score (82 High) indicate severe exposure. Notably uncovered during automated AI-assisted red-team audits conducted jointly by ENISA and CERT-EU, this flaw illustrates how lack of single-use token invalidation converts transient network eavesdropping into persistent account takeover.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-73431: CIRCL Vulnerability-Lookup Stateless Token Replay Account TakeoverVULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTMicrosoft Office & 365 Apps

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Microsoft Office & 365 Apps documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Discovery Milestone: ENISA & CERT-EU AI-Assisted Audit

Uncovered via Advanced AI Security Auditing: CVE-2026-73431 was identified during proactive software evaluation research performed by the European Union Agency for Cybersecurity (ENISA) in collaboration with CERT-EU, leveraging frontier AI models to audit critical open-source cybersecurity infrastructure.

Executive Summary

CVE-2026-73431 is an authentication bypass and account takeover vulnerability affecting vulnerability-lookup versions up to and including 5.5.1 (developed by the Computer Incident Response Center Luxembourg — CIRCL). The software generated stateless cryptographically signed tokens for account activation and password resets without tracking whether a token had already been consumed. An attacker intercepting an activation or recovery URL can replay the token repeatedly throughout the configured TOKEN_VALIDITY_PERIOD, overriding passwords even after legitimate users have completed their reset. Remediation requires upgrading to version 6.0.0 or later.

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1. Technical Root Cause: Stateless Tokens & Missing Purpose Binding

In vulnerability-lookup <= 5.5.1, user registration and password recovery workflows generated stateless signed tokens (using cryptographic timestamp signers):

sequenceDiagram
    autonumber
    actor User as Legitimate Analyst
    actor Attacker as Eavesdropping Adversary
    participant App as Vulnerability-Lookup Server
    participant DB as Backend Database

    User->>App: Requests password reset (/reset_password)
    App-->>User: Dispatches email with signed token T
    Attacker->>User: Intercepts token T via proxy/eavesdropping
    User->>App: Submits token T with NewPassword_User
    App->>DB: Updates password (Token T NOT marked as consumed)
    Note over App,DB: Token T remains valid for 24-72h!
    Attacker->>App: Replays token T with AttackerPassword
    App->>DB: Overrides password again - Account successfully hijacked!

The flaw results from two core architectural oversights:

1. No Single-Use Invalidation: The server verified the cryptographic signature and timestamp of the token against TOKEN_VALIDITY_PERIOD, but maintained zero persistent state tracking used tokens. Once generated, a token could be submitted arbitrarily many times until its absolute expiration.
2. Missing Purpose Binding: Tokens lacked explicit intent scoping (action="activation" vs action="reset"), allowing token type confusion across different endpoints.

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2. Commit Resolution Analysis (bef837242657)

CIRCL remediated the vulnerability in commit bef837242657acf680832be56b94428df130ed67 by introducing:

• Random Cryptographic Nonces: A high-entropy random nonce is generated per token request.
• SHA-256 Nonce Hashing: The SHA-256 digest of the active nonce is recorded in the user’s database document.
• Atomic Single-Use Invalidation: When a password change or activation completes, the stored nonce is immediately rotated or cleared, rendering the token instantly invalid.
• Explicit Action Scoping: Tokens must explicitly declare and match the targeted action.

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3. Forensic Analysis & Detection Rules

3.1 Web Server Log Detection (Nginx / Apache)

Identify tokens submitted more than once to authentication endpoints:

grep -E "POST /(activate|reset_password)" /var/log/nginx/access.log \
  | grep -o "token=[^ &]*" \
  | sort | uniq -c | sort -nr | awk '$1 > 1'

(Any token appearing multiple times with successful 200 OK or 302 Found responses from distinct client IP addresses indicates an active replay attack).

3.2 Audit Log Tripwires

Examine application logs for rapid successive password_reset_success events for identical account handles within short timeframes.

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4. Remediation & Hardening

1. Upgrade Immediately: Upgrade your vulnerability-lookup deployment to version 6.0.0 or later.
2. Temporary Mitigation (Pre-Patch): Shorten TOKEN_VALIDITY_PERIOD in your application configuration to a minimal window:

   TOKEN_VALIDITY_PERIOD = 300  # 5 minutes instead of 86400s

3. Session Invalidation: Upon applying the patch, revoke all active sessions and force password resets across analyst accounts if proxy logs show token reuse.

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5. References

• Upstream Advisory & Commit: CIRCL bef837242657acf680832be56b94428df130ed67
• Fixed Version: vulnerability-lookup Release 6.0.0
• Auditing Bodies: European Union Agency for Cybersecurity (ENISA) & CERT-EU
• Related Hermes Intelligence:
  • Hermes Threat Score Methodology
  • Vulnerability Genome Architecture