CVE-2026-55430: Coder improper X-Forwarded-Host validation in workspace app proxy

CVE-2026-55430 · Severity: medium · CVSS 5.8 · Published 2026-07-08

Coder is a platform used by organizations to manage and deploy remote development environments. A security flaw in how the system handles web requests could allow an attacker to trick the system into granting them access to another user's private development tools. If a victim visits a malicious application shared on the platform, the attacker could potentially view or interact with the victim's private workspace data.

Technologies: Coder, github.com/coder/coder (Go), github.com/coder/coder/v2 (Go). Vendors: Coder, Go.

Quick answers

Is CVE-2026-55430 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55430 being exploited in the wild.
How severe is CVE-2026-55430?
Medium severity, with a CVSS score of 5.8, published 8 July 2026.
Which products and versions are affected?
Coder < 2.29.17, >= 2.30.0 < 2.32.7, >= 2.33.0 < 2.33.8, >= 2.34.0 < 2.34.2, < 2.29.17, >= 2.30.0, < 2.32.7, >= 2.33.0, < 2.33.8, >= 2.34.0, < 2.34.2; github.com/coder/coder (Go) SEMVER:introduced=0; github.com/coder/coder/v2 (Go) SEMVER:introduced=0,fixed=2.29.17,introduced=2.30.0,fixed=2.32.7,introduced=2.33.0,fixed=2.33.8,introduced=2.34.0,fixed=2.34.2, SEMVER:introduced=2.34.0,fixed=2.34.2.
Is there a fix for CVE-2026-55430?
Yes. github.com/coder/coder/v2 (Go): upgrade to 2.34.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55430 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-55430?
Check whether you run Coder, github.com/coder/coder (Go) or github.com/coder/coder/v2 (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/coder/coder/v2 (Go): upgrade to 2.34.2 or later
    go get github.com/coder/coder/v2@v2.34.2

Technical details

A 'Confused Deputy' vulnerability exists in Coder's workspace app proxy where the system resolves target applications using the `X-Forwarded-Host` header without proper validation. Because this header is not browser-forbidden, an attacker can use client-side JavaScript (via `fetch()`) within a shared authenticated app to forge the header and point to a victim's private app. Since session cookies are scoped to the wildcard apps domain, the proxy may authorize and route the request as the victim, returning private app content to the attacker's origin. Exploitation requires subdomain app routing (wildcard hostnames) to be enabled and an upstream proxy that does not strip the malicious header. The fix ensures `X-Forwarded-Host` is only trusted from configured trusted proxies.

Affected products

  • Coder Coder < 2.29.17, >= 2.30.0 < 2.32.7, >= 2.33.0 < 2.33.8, >= 2.34.0 < 2.34.2

Identifiers

  • CVE-2026-55430
  • GHSA-5g4w-3vw9-478w
  • GO-2026-5917

Timeline

  • 2026-06-11: patched: Fix merged into main branch
  • 2026-06-12: advisory: Security release v2.29.17 published
  • 2026-07-08: disclosed: CVE published to NVD

References

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