CVE-2026-85394 — python-jose
CVE-2026-85394 is a CWE-347 vulnerability in python-jose. No vendor fix is recorded yet; mitigation options are listed below.
python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-85394.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
python-joseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | python-jose | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for python-jose, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of python-jose has shipped for CVE-2026-85394 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
1. **Attack complexity is higher than AC:L suggests**: While the CVSS vector claims AC:L, successful exploitation requires: - The service must accept multiple signature algorithms (RS256 + HS256) during JWT verification, either explicitly via `algorithms=['RS256', 'HS256']` or implicitly via `algorithms=None` (the…
This flaw can be mitigated by strictly restricting the signature algorithms accepted during JWT verification. Applications using python-jose should always pass an explicit allow-list containing only the intended asymmetric algorithms (for example, algorithms=["RS256"]) when calling jose.jwt.decode(), must not include HMAC algorithms such as HS256 in that list, and must not rely on the default algorithms=None behavior, which permits multiple algorithms. The algorithm-confusion attack requires that HMAC verification be accepted alongside public-key verification, so removing HMAC algorithms from the accepted set prevents an attacker from using the service's public key as an HMAC shared secret…Source: Red Hat security advisory for CVE-2026-85394 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-85394 in your dependencies?
Find it across PyPI, including transitive dependencies.