# PyJWT: Uncaught RecursionError in jwt.decode() on deeply nested token header

Advisory record · `GHSA-8wjv-2p76-3863`

- **Identifiers:** `GHSA-8wjv-2p76-3863` · `CVE-2026-102265` · `PYSEC-2026-4142`
- **State:** Confirmed
- **Severity:** CVSS 5.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-674](https://cwe.mitre.org/data/definitions/674.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 29 Sept 2026
- **Updated:** 1 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 29 Sept 2026, 23:43 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `pyjwt` (PyPI): affected `>=2.13.0, <2.14.0`; fixed in `2.14.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> PyJWT versions 2.13.0 up to but not including 2.14.0 are affected. When a JWT's header contains deeply nested JSON, jwt.decode() raises a RecursionError, which is not a PyJWTError, so applications that catch only PyJWT errors can fail with a server error. An unauthenticated attacker can trigger this with a single crafted unsigned token, causing repeated denial of service on token-validating endpoints. Upgrade to PyJWT 2.14.0, which translates this error into DecodeError.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0034, the 28th percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:09 UTC: First seen by agentprime
- 31 Oct 2026, 14:09 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-8wjv-2p76-3863)

## Sources

- [GitHub Advisory Database: GHSA-8wjv-2p76-3863](https://github.com/advisories/GHSA-8wjv-2p76-3863)
- [OSV: GHSA-8wjv-2p76-3863](https://osv.dev/vulnerability/GHSA-8wjv-2p76-3863)
- <https://github.com/jpadilla/pyjwt/security/advisories/GHSA-8wjv-2p76-3863>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-102265>
- <https://github.com/jpadilla/pyjwt/commit/06573692ebcdec8831c3927513b3e87c31fbbb62>
- <https://github.com/jpadilla/pyjwt>
- <https://github.com/jpadilla/pyjwt/releases/tag/2.14.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-8wjv-2p76-3863>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-8wjv-2p76-3863/>. Everything for agents: <https://agentprime.io/llms.txt>.