🛡️ CVE-2026-55438 — coder

🟡 CVSS 5.8 — Medium ✅ No Known Exploit CWE-346 NVD
5.8
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

Summary

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.

> Note: Practical exploitation requires subdomain app routing (wildcard hostname) enabled and a victim who visits the attacker's crafted app URL while authenticated.

Impact

An 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.

Patches

The fix validates the subdomain username against the resolved workspace's actual owner and bases the same-owner CORS decision on the authoritative owner identity.

The fix was backported to all supported release lines:

| Release line | Patched version |

|---|---|

| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |

| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |

| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |

| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |

Workarounds

None.

Resources

  • Fix: #26086, #26085

Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-22434) for independently disclosing this issue!

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs low-level privileges on the target. A user must be tricked into taking some action. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality high, integrity none, availability none.

Weakness class

CVE-2026-55438 is classified as CWE-346: Origin Validation Error. The origin of a message or request is not verified properly, so one source can pose as another.

Affected software

CVE-2026-55438 is recorded against 3 packages.

  • coder (from 2.34.0 up to 2.34.2)
  • github.com/coder/coder
  • github.com/coder/coder/v2

Timeline and source

Published on 8 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com
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Details

Severity MEDIUM
CVSS Score 5.8
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N
CWE CWE-346
Public Exploit ✅ No
Source NVD
Published 2026-07-08
Updated 2026-08-12
Modified 2026-07-08

Affected Packages

Software From version Fixed in
coder 2.34.0 2.34.2
github.com/coder/coder — —
github.com/coder/coder/v2 — —

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