Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-55438Coder's workspace app CORS origin check can be bypassed via UUID-based subdomain spoofing

Medium 5.8

In plain English

A medium-severity security flaw in coder from coder. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.8Medium

Exploit odds (30 days)0.2%top 87.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Coder allows organizations to provision remote development environments via Terraform. Prior to versions 2.29.17, 2.32.7, 2.33.8, and 2.34.2, Coder's subdomain-based workspace app proxy allowed the same-owner CORS check to be bypassed. When a workspace-name subdomain segment parsed as a UUID, the workspace was resolved by ID without confirming the URL's username matched the real owner, while the CORS middleware trusted the unverified username in the hostname. Practical exploitation requires subdomain app routing (wildcard hostname) enabled and a victim who visits the attacker's crafted app URL while authenticated. The fix in versions 2.29.17, 2.32.7, 2.33.8, and 2.34.2 validates the subdomain username against the resolved workspace's actual owner and bases the same-owner CORS decision on the authoritative owner identity. No known workarounds are available.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/coder/coder	no fix listed	GO-2026-5918
Go	github.com/coder/coder/v2	2.34.2	GHSA-5wg6-jmq2-53pw
Go	github.com/coder/coder/v2	2.33.8	GHSA-5wg6-jmq2-53pw
Go	github.com/coder/coder/v2	2.32.7	GHSA-5wg6-jmq2-53pw
Go	github.com/coder/coder/v2	2.29.17	GHSA-5wg6-jmq2-53pw
Go	github.com/coder/coder/v2	2.29.17, 2.32.7, 2.33.8, 2.34.2	GO-2026-5918

Affected products (as reported)

Vendor	Product	Versions
coder	coder	>= 2.34.0, < 2.34.2>= 2.33.0, < 2.33.8>= 2.30.0, < 2.32.7< 2.29.17

Weakness: CWE-346 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N

References

https://github.com/coder/coder/security/advisories/GHSA-5wg6-jmq2-53pw x_refsource_CONFIRM
https://github.com/coder/coder/pull/26085 x_refsource_MISC
https://github.com/coder/coder/pull/26086 x_refsource_MISC
https://github.com/coder/coder/releases/tag/v2.29.17 x_refsource_MISC
https://github.com/coder/coder/releases/tag/v2.32.7 x_refsource_MISC
https://github.com/coder/coder/releases/tag/v2.33.8 x_refsource_MISC
https://github.com/coder/coder/releases/tag/v2.34.2 x_refsource_MISC