pac4j-jwt: Improper Verification of Cryptographic Signature
CVE-2026-29000 is a critical-severity improper verification of cryptographic signature vulnerability in pac4j-jwt from Pac4j, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 4.5.9, 5.7.9, 6.3.3 as the first without the flaw, so updating pac4j-jwt to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 6.17% chance of exploitation within 30 days, which is in the top 6.4% of all scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update pac4j-jwt to 4.5.9 or 5.7.9 or 6.3.3, whichever matches your release line, or a later version.
- Read the advisory on pac4j.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Pac4j | pac4j-jwt | 4.0 up to, but not including, 4.5.9; 5.0 up to, but not including, 5.7.9; 6.0 up to, but not including, 6.3.3 | 4.5.9, 5.7.9, 6.3.3 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CNA (vulncheck.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (vulncheck.com) |
| CVSS 3.1 | 9.1 | Critical | CNA (vulncheck.com) |
Official description
pac4j-jwt versions prior to 4.5.9, 5.7.9, and 6.3.3 contain an authentication bypass vulnerability in JwtAuthenticator when processing encrypted JWTs that allows remote attackers to forge authentication tokens. Attackers who possess the server's RSA public key can create a JWE-wrapped PlainJWT with arbitrary subject and role claims, bypassing signature verification to authenticate as any user including administrators.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Verification of Cryptographic Signature
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
More Improper Verification of Cryptographic Signature vulnerabilities (CWE-347)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
Recent Improper Verification of Cryptographic Signature vulnerabilities
- 7.5 High severity
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- 8.1 High severity
- 8.1 High severity
- 7.5 High severity
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