# Contour has Improper JWT Verification for Non-SNI Requests on Virtual Hosts with Fallback Certificate Enabled

Advisory record · `GHSA-g3xr-5w5j-w4q4`

- **Identifiers:** `GHSA-g3xr-5w5j-w4q4` · `BIT-contour-2026-50149` · `CVE-2026-50149` · `GO-2026-5889`
- **State:** Confirmed
- **Severity:** CVSS 6.5 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-295](https://cwe.mitre.org/data/definitions/295.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md)
- **Published:** 2 Jul 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 2 Jul 2026, 17:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/projectcontour/contour` (Go): affected `>=1.23.0, <1.33.5`; fixed in `1.33.5`

## Machine-written summary

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

> Contour, the Go package github.com/projectcontour/contour in versions 1.23.0 through before 1.33.5, does not reject HTTPProxy resources that set both enableFallbackCertificate and jwtProviders on a virtual host. Clients that send no TLS SNI or an unrecognized SNI can bypass JWT verification and reach upstream services without a valid token, so an attacker needs only network access to the affected listener. Upgrade to version 1.33.5, which marks such resources invalid; as a workaround, remove either the fallback certificate setting or the JWT providers from affected HTTPProxy resources.

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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0019, the 8th percentile, on 11 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:14 UTC: First seen by agentprime
- 31 Oct 2026, 14:14 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-g3xr-5w5j-w4q4)

## Sources

- [GitHub Advisory Database: GHSA-g3xr-5w5j-w4q4](https://github.com/advisories/GHSA-g3xr-5w5j-w4q4)
- [OSV: GHSA-g3xr-5w5j-w4q4](https://osv.dev/vulnerability/GHSA-g3xr-5w5j-w4q4)
- <https://github.com/projectcontour/contour/security/advisories/GHSA-g3xr-5w5j-w4q4>
- <https://github.com/projectcontour/contour>

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-g3xr-5w5j-w4q4>, 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-g3xr-5w5j-w4q4/>. Everything for agents: <https://agentprime.io/llms.txt>.