{"id":"CVE-2026-55438","aliases":["GHSA-5wg6-jmq2-53pw"],"title":"Coder's workspace app CORS origin check can be bypassed via UUID-based subdomain spoofing","summary":"Coder's workspace app CORS origin check can be bypassed via UUID-based subdomain spoofing","severity":"medium","cvss":5.8,"cwe":["CWE-346"],"vendor":"coder","product":"github.com/coder/coder/v2","ecosystem":"go","affected":["github.com/coder/coder/v2 >= 2.34.0, < 2.34.2","github.com/coder/coder/v2 >= 2.33.0, < 2.33.8","github.com/coder/coder/v2 >= 2.30.0, < 2.32.7","github.com/coder/coder/v2 < 2.29.17"],"patched":["github.com/coder/coder/v2 2.34.2","github.com/coder/coder/v2 2.33.8","github.com/coder/coder/v2 2.32.7","github.com/coder/coder/v2 2.29.17"],"published":"2026-07-06","updated":"2026-07-06","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-5wg6-jmq2-53pw","references":[{"url":"https://github.com/coder/coder/security/advisories/GHSA-5wg6-jmq2-53pw"},{"url":"https://github.com/coder/coder/pull/26085"},{"url":"https://github.com/coder/coder/pull/26086"},{"url":"https://github.com/advisories/GHSA-5wg6-jmq2-53pw"}],"tags":["ghsa","go"],"ingestedAt":"2026-07-06T21:45:52.938Z","epss":0.00222,"epssPercentile":0.13066,"slug":"CVE-2026-55438","body":"## Overview\n\n### Summary\n\nCoder'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.\n\n> **Note:** Practical exploitation requires subdomain app routing (wildcard hostname) enabled and a victim who visits the attacker's crafted app URL while authenticated.\n\n### Impact\n\nAn authenticated user could craft a subdomain encoding their own workspace UUID and a victim's username. If the victim visited the attacker's URL, the attacker's JavaScript could issue credentialed cross-origin `fetch()` requests to the victim's workspace apps and read the responses, exfiltrating data accessible through those apps.\n\n### Patches\n\nThe fix validates the subdomain username against the resolved workspace's actual owner and bases the same-owner CORS decision on the authoritative owner identity.\n\nThe fix was backported to all supported release lines:\n\n| Release line | Patched version |\n|---|---|\n| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |\n| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |\n| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |\n| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |\n\n### Workarounds\n\nNone.\n\n### Resources\n\n- Fix: #26086, #26085\n\n### Credits\n\nCoder would like to thank Anthropic's Security Team (ANT-2026-22434) for independently disclosing this issue!\n\n## Affected packages\n\n- `github.com/coder/coder/v2 >= 2.34.0, < 2.34.2`\n- `github.com/coder/coder/v2 >= 2.33.0, < 2.33.8`\n- `github.com/coder/coder/v2 >= 2.30.0, < 2.32.7`\n- `github.com/coder/coder/v2 < 2.29.17`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/coder/coder/v2 2.34.2`\n- `github.com/coder/coder/v2 2.33.8`\n- `github.com/coder/coder/v2 2.32.7`\n- `github.com/coder/coder/v2 2.29.17`","depth":"sunlit","depthScore":32,"depthScoreParts":{"impact":31.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}