EUVD-2026-72912
GHSA-3464-x248-vrcx
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessEnumerate or register to learn target username
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DeliveryCompute JWT secret from username + current month
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ExploitSign forged token with elevated role claims
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ExecutionSubmit forged token to authenticated API endpoints
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ImpactAccess or modify data as impersonated user
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A04:2025 - Cryptographic Failures
ASVS 5.0
V11 - Cryptography Cryptographic random values
|
| Exploitation Conditions | The attacker must know or enumerate at least one target username; registration flows in exam platforms commonly expose usernames via profile pages, email confirmation, or login-error enumeration. The current calendar month is a public value. No elevated privileges, special network position, or victim interaction is required - any attacker capable of sending HTTP requests to the application can exploit this. The only practical constraint is knowledge of the target username; exploitation is not possible against accounts with completely unknowable usernames. The derivation formula is now effectively public via the GitHub writeup, removing any security-through-obscurity barrier that previously existed. |
| Impact | The provided CVSS 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) captures network accessibility and high confidentiality impact but the I:N rating appears to understate actual risk: JWT forgery fundamentally enables impersonation and privilege escalation to any account whose username is known, including administrators, which is a meaningful integrity impact. EPSS at 0.14% (4th percentile) reflects low automated exploitation probability, consistent with a niche product. No active exploitation is confirmed - not in CISA KEV. Despite the low EPSS, the technical exploitation difficulty is essentially zero once the formula is known: a competent attacker can forge a valid admin token in seconds. Real-world risk is therefore primarily bounded by yfexam-exam's limited deployment footprint rather than technical barriers. The mismatch between the trivial exploitation path and the 'only' 7.5 CVSS score (driven by I:N) is a notable data quality concern. |
| Exploit ScenarioDerived | An attacker registers an account on yfexam-exam, notes their own username and the current month, and computes the signing secret using the now-public derivation formula from the GitHub writeup. Using that secret, they sign a forged JWT claiming the identity or role of an administrator, submit it to the application API, and gain full admin access - entirely without the admin's credentials or any interaction from a victim user. |
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Alert meAnalysisAIv1 – Sep 09, 2026
JWT token forgery in yfexam-exam v2.0 exposes any authenticated session to impersonation because the signing secret is derived entirely from the username and the current calendar month - two low-entropy, often-public values - rather than a server-side cryptographic secret. An attacker who knows or can enumerate a target's username can deterministically compute the signing secret (only 12 possible month values) and mint forged tokens claiming arbitrary privileges without ever knowing the target's password. No active exploitation is confirmed (not in CISA KEV), and EPSS sits at 0.14% (4th percentile), but a public GitHub writeup by fangtang7 documents the technique, materially lowering the bar for any attacker who targets this application.
RemediationAI
Replace the predictable JWT signing secret derivation with a cryptographically random server-side secret of at least 256 bits, generated once at deployment using a CSPRNG (e.g., OpenSSL rand, /dev/urandom, or a framework-native secret generator) and stored securely in server-side configuration - never derived from user-controlled or time-based inputs. No vendor-released patch has been identified at time of analysis; the GitHub writeup documents the flaw but references no upstream fix. As compensating controls until patching is possible: enforce short JWT expiration windows (minutes, not hours) to limit the forged-token validity window; implement server-side token revocation or session binding (e.g., tie tokens to IP or user-agent hash with re-validation); restrict the application to internal network access if external exposure is not required. Note that expiration shortening reduces usability and does not eliminate the core forgery risk.
Affected VersionsENISA
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Technical ContextAI · show details
JWT (JSON Web Token) authentication security rests entirely on the secrecy and unpredictability of the server-side signing key. CWE-330 (Use of Insufficiently Random Values) captures the root cause: yfexam-exam v2.0 derives the signing secret from deterministic, low-entropy inputs - the username and current calendar month - instead of a cryptographically random value generated at deployment time. The month component collapses the search space to at most 12 values; the username is either already known (one's own account) or potentially discoverable through registration flows or user enumeration. Once the derivation formula is known (now public via the GitHub writeup), the secret is directly computable, not merely brute-forceable. No valid CPE identifier exists for this product (EUVD lists 'n/a n/a'), which limits automated vulnerability management tooling coverage.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Formula is public and month-space is 12 values, making secret directly computable; I:H added because token forgery enables arbitrary user impersonation and privilege escalation.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
Lifecycle Timeline
3DescriptionCVE.org
The JWT signing secret in yfexam-exam v2.0 is derived from the username and the current month instead of a random server-side key, making the secret key easily obtainable via a bruteforce attack.
Executive ViewAI
yfexam-exam v2.0 contains an authentication vulnerability allowing attackers to impersonate any user account without passwords or valid credentials. Publicly available exploit code exists for this attack. Organizations using this exam platform face immediate risk of exam manipulation, credential theft, and unauthorized administrative access.
No vendor-released patch identified at time of analysis. Interim mitigations: restrict network access via firewall/VPN to limit attacker reach; implement comprehensive authentication and session logging to detect unauthorized activity; deploy Web Application Firewall rules to flag token forgery attempts; enforce aggressive session timeouts and token rotation; enable multi-factor authentication as an additional verification layer; conduct forensic audit of authentication logs for unauthorized access patterns; plan immediate upgrade to version beyond v2.0 or migration to alternative platform once a remediated version becomes available.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.
Exploit-DB