Security Digest · Vulnerability record
CVE-2026-85394: python-jose algorithm confusion guard bypassed by DER-encoded public keys
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.
CVSS 9.3 Critical EPSS 0.2% · p12
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.2%, percentile 12: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 12% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
python-jose(PyPI) <= 3.5.0, no fixed version listed. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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.
Weakness type: CWE-347.
Product: python-jose (PyPI) · Assigned by: VulnCheck · Published: 2026-09-03
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| PyPI | python-jose | <= 3.5.0 | none listed |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| mpdavis | python-jose | <= 3.5.0 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| VulnCheck | 4.0 | 9.3 Critical | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N |
| VulnCheck | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| GitHub | 4.0 | 9.3 | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Attack requirements: none
- Privileges required: none (no login)
- User interaction: none
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.22% probability of exploitation activity in the next 30 days; percentile 12.
Timeline
- — CVE record published by VulnCheck
- — GitHub-reviewed advisory GHSA-3qf3-8w2g-rqmx published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-3qf3-8w2g-rqmx github.com
- CVE.org record CVE-2026-85394 cve.org
- NVD entry CVE-2026-85394 nvd.nist.gov
Other references from the CVE record and advisory
- GitHub Issue #414 github.com
- github.com github.com
- github.com github.com
- github.com github.com
- GitHub Security Advisory (GHSA-6c5p-j8vq-pqhj) github.com
- VulnCheck Advisory: python-jose through 3.5.0 Algorithm Confusion via DER-encoded Public Key as HMAC Secret vulncheck.com