CVE-2026-55438 Coder's workspace app CORS origin check can be bypassed via UUID-based subdomain spoofing
Attackers can bypass CORS checks in Coder's workspace proxy by spoofing UUID-based subdomains, requiring subdomain routing enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-55438?
CVE-2026-55438 is a medium-severity vulnerability in coder, published on 8 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
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.
Weakness: CWE-346
Which versions are affected by CVE-2026-55438?
10 open source packages ship an affected version, including github.com/coder/coder/v2 and github.com/coder/coder. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/coder/coder/v2 Go | All versions | 2.29.17, 2.32.7, 2.33.8, 2.34.2 |
github.com/coder/coder/v2 Go | All versions | 2.29.17 |
github.com/coder/coder/v2 Go | All versions | 2.29.17 |
github.com/coder/coder/v2 Go | From 2.30.0 | 2.32.7 |
github.com/coder/coder/v2 Go | From 2.30.0 | 2.32.7 |
github.com/coder/coder/v2 Go | From 2.33.0 | 2.33.8 |
4 more packages
github.com/coder/coder/v2 Go | From 2.33.0 | 2.33.8 |
github.com/coder/coder/v2 Go | From 2.34.0 | 2.34.2 |
github.com/coder/coder/v2 Go | From 2.34.0 | 2.34.2 |
github.com/coder/coder Go | All versions | None |
Products include Coder Coder.
How do I fix CVE-2026-55438?
Upgrade github.com/coder/coder/v2 to a fixed version for your release line: 2.29.17, 2.32.7, 2.33.8 or 2.34.2.
Is CVE-2026-55438 being exploited?
There is no known exploitation of CVE-2026-55438 in the wild and no public exploit code.
Other vulnerabilities in coder
- CVE-2026-46354 Coder: PKCS#7 signature bypass in Azure instance identity allows unauthenticated agent token theft
- CVE-2026-55429 Coder's workspace app upsert allows cross-workspace agent rebinding via user-controlled app ID
- CVE-2026-55427 Coder vulnerable to SSH config injection via unsanitized server-supplied values in `coder config-ssh`
- CVE-2026-55428 Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator
- CVE-2024-27918 Coder's OIDC authentication allows email with partially matching domain to register
Sources
Also known as GHSA-5wg6-jmq2-53pw, GO-2026-5918.