# 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. - **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N`) - **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:** Yes - **Published:** 8 Jul 2026 - **Updated:** 8 Jul 2026 - **Also known as:** GHSA-5wg6-jmq2-53pw, GO-2026-5918 ## 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 (Origin Validation Error) ## 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 | Ecosystem | 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 | | `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: 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](https://insights.sbomify.com/CVE-2026-46354/): Coder: PKCS#7 signature bypass in Azure instance identity allows unauthenticated agent token theft (critical 9.1) - [CVE-2026-55429](https://insights.sbomify.com/CVE-2026-55429/): Coder's workspace app upsert allows cross-workspace agent rebinding via user-controlled app ID (high 8.7) - [CVE-2026-55427](https://insights.sbomify.com/CVE-2026-55427/): Coder vulnerable to SSH config injection via unsanitized server-supplied values in `coder config-ssh` (high 8.3) - [CVE-2026-55428](https://insights.sbomify.com/CVE-2026-55428/): Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator (high 8.2) - [CVE-2024-27918](https://insights.sbomify.com/CVE-2024-27918/): Coder's OIDC authentication allows email with partially matching domain to register (high 8.2) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-55438 and fix it if it is affected. What it is: 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. Exploitation: There is no known exploitation of CVE-2026-55438 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/coder/coder/v2 (Go): affected all versions; fixed in 2.29.17, 2.32.7, 2.33.8, 2.34.2 - github.com/coder/coder/v2 (Go): affected all versions; fixed in 2.29.17 - github.com/coder/coder/v2 (Go): affected all versions; fixed in 2.29.17 - github.com/coder/coder/v2 (Go): affected from 2.30.0; fixed in 2.32.7 - github.com/coder/coder/v2 (Go): affected from 2.30.0; fixed in 2.32.7 - github.com/coder/coder/v2 (Go): affected from 2.33.0; fixed in 2.33.8 - github.com/coder/coder/v2 (Go): affected from 2.33.0; fixed in 2.33.8 - github.com/coder/coder/v2 (Go): affected from 2.34.0; fixed in 2.34.2 - github.com/coder/coder/v2 (Go): affected from 2.34.0; fixed in 2.34.2 - github.com/coder/coder (Go): affected all versions; no fix listed Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-55438/ (Markdown: https://insights.sbomify.com/CVE-2026-55438/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55438 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55438 - OSV: https://osv.dev/vulnerability/CVE-2026-55438 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-55438/ Summaries are generated and may contain mistakes; the official description above is the record.