EUVD-2026-42151
GHSA-5wg6-jmq2-53pw
Severity by source
AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N
Requires non-default wildcard subdomain config (AC:H), authenticated attacker account (PR:L), victim browser visit (UI:R), crosses workspace ownership boundary (S:C), full read of victim app responses (C:H), no write or availability impact.
Primary rating from Vendor (https://github.com/coder/coder).
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N
Lifecycle Timeline
2DescriptionNVD
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:
Workarounds
None.
Resources
- Fix: #26086, #26085
Credits
Coder would like to thank Anthropic's Security Team (ANT-2026-22434) for independently disclosing this issue!
AnalysisAI
Cross-origin request forgery via CORS same-owner bypass in Coder's subdomain workspace app proxy allows an authenticated attacker to exfiltrate data from a victim's workspace apps. The flaw exists across Coder release lines 2.29 through 2.34, and was disclosed by Anthropic's Security Team. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Three conditions must simultaneously hold for exploitation: (1) the Coder deployment must have wildcard subdomain routing enabled for workspace app proxying - this is not a default configuration and must be explicitly configured by administrators; (2) the attacker must be an authenticated Coder user holding their own workspace, providing a valid workspace UUID to embed in the crafted subdomain; (3) a victim must actively visit the attacker's crafted subdomain URL while authenticated to the same Coder deployment. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS 3.1 score of 5.8 (AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N) accurately reflects the attack's meaningful prerequisites. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with a valid Coder account creates their own workspace to obtain a workspace UUID, then crafts a subdomain URL embedding their UUID alongside a victim's username to satisfy the ID-based lookup path while misleading the CORS middleware. The attacker delivers this link to the victim via phishing or social engineering; when the victim visits the URL while authenticated to the same Coder deployment, the attacker's JavaScript executes in a context the CORS middleware treats as same-owner and issues credentialed fetch() calls to the victim's workspace apps, reading and exfiltrating the full response bodies. |
| Remediation | Upgrade to the vendor-released patched versions: v2.34.2 for the 2.34 release line, v2.33.8 for the 2.33 line, v2.32.7 for the 2.32 line, or v2.29.17 for the 2.29 ESR line, all available at https://github.com/coder/coder/releases. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-346 – Origin Validation Error
View allSame technique Authentication Bypass
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External POC / Exploit Code
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