CVE-2026-48525

Description

PyJWT is a JSON Web Token implementation in Python. From 2.8.0 to 2.12.1, when verifying detached JWS tokens using the unencoded-payload option ("b64": false, RFC 7797), PyJWT performs Base64URL decoding of the compact-serialization payload segment before enforcing the detached-payload rules. For b64=false, PyJWT later discards that decoded payload and replaces it with the caller-provided detached_payload. In practice, this turns the middle segment into an attacker-controlled “work amplifier”: a remote client can supply an arbitrarily large Base64URL payload segment that forces CPU work + memory allocations even if the signature is invalid. This creates an unauthenticated DoS vector against any endpoint that verifies detached JWS using PyJWT. This vulnerability is fixed in 2.13.0.

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CVSS v3.1 Score

5.3

MEDIUM

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

EPSS — Exploit Prediction

0.0025

Probability of exploitation

0.16%

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-400 Uncontrolled Resource Consumption

Affected Products

Vendor	Product	Versions
pyjwt_project	pyjwt	2.8.0 — 2.12.1

References

Advisories & Patches

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39 https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39

Exploits

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39 https://github.com/jpadilla/pyjwt/security/advisories/GHSA-w7vc-732c-9m39

Frequently Asked Questions

What is CVE-2026-48525? +

PyJWT is a JSON Web Token implementation in Python. From 2.8.0 to 2.12.1, when verifying detached JWS tokens using the unencoded-payload option ("b64": false, RFC 7797), PyJWT performs Base64URL decoding of the compact-serialization payload segment before enforcing the detached-payload rules. For b64=false, PyJWT later discards that decoded payload and replaces it with the caller-provided detached_payload. In practice, this turns the middle segment into an attacker-controlled “work amplifier”: a remote client can supply an arbitrarily large Base64URL payload segment that forces CPU work + memory allocations even if the signature is invalid. This creates an unauthenticated DoS vector against any endpoint that verifies detached JWS using PyJWT. This vulnerability is fixed in 2.13.0. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-48525? +

CVE-2026-48525 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0025, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-48525? +

CVE-2026-48525 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-2026-48525? +

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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