CVE-2026-48523

Description

PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.

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CVSS v3.1 Score

5.4

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0011

Probability of exploitation

0.02%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-347 CWE-347

Affected Products

Vendor	Product	Versions
pyjwt_project	pyjwt	2.9.0 — 2.12.1

References

Advisories & Patches

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f

Exploits

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f

Frequently Asked Questions

What is CVE-2026-48523? +

PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-48523? +

CVE-2026-48523 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0011, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-48523? +

CVE-2026-48523 affects products from pyjwt_project, specifically: pyjwt. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-48523? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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