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Advisory record · GHSA-g3xr-5w5j-w4q4

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

CVSS 6.5 MediumEPSS 0.0019 · 8th percentile

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.

PackageEcosystemAffectedFixed in
github.com/projectcontour/contourGo>=1.23.0, <1.33.51.33.5
Identifiers
GHSA-g3xr-5w5j-w4q4 · BIT-contour-2026-50149 · CVE-2026-50149 · GO-2026-5889
Weakness (CWE)
CWE-295
Tags
Published
2 Jul 2026
Updated
10 Sept 2026

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

ScoreRatingCVSSVectorSource
6.5 Medium 3.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N 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

  1. 31 Oct 2026, 14:14 UTC First seen by agentprime
  2. 31 Oct 2026, 14:14 UTC Confirmed by OSV

Sources

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.