CVE-2026-55079

Coder's unbounded memory allocation in provisioner file upload allows authenticated denial of service

NewDataBuilder in provisionersdk/proto/dataupload.go allocated a byte slice using the client-supplied FileSize from a DataUpload message without an upper-bound check. Although the DRPC wire limit is 4 MiB, the FileSize value itself was unconstrained

Workarounds

Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts.

Resources

• Fix: #25710

Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-22442) for independently disclosing this issue!

An authenticated user able to reach the provisioner daemon serve endpoint could send a roughly 50-byte message declaring a huge FileSize (for example 1 TiB), triggering an unrecoverable Go out-of-memory abort that terminates coderd. This is a single-message denial of service affecting the entire deployment.

CVE-2026-55079 has a CVSS score of 4.9 (Medium). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.34.2, 2.33.8, 2.32.7, 2.29.17); upgrading removes the vulnerable code path.

Kodem intelligence

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The fix validates FileSize against an upper bound (MaxFileSize = 100 MiB) before allocation.

The fix was backported to all supported release lines:

1. What is CVE-2026-55079? CVE-2026-55079 is a medium-severity security vulnerability in github.com/coder/coder/v2 (go), affecting versions >= 2.34.0, < 2.34.2. It is fixed in 2.34.2, 2.33.8, 2.32.7, 2.29.17.
2. How severe is CVE-2026-55079? CVE-2026-55079 has a CVSS score of 4.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/coder/coder/v2 are affected by CVE-2026-55079? github.com/coder/coder/v2 (go) versions >= 2.34.0, < 2.34.2 is affected.
4. Is there a fix for CVE-2026-55079? Yes. CVE-2026-55079 is fixed in 2.34.2, 2.33.8, 2.32.7, 2.29.17. Upgrade to this version or later.
5. Is CVE-2026-55079 exploitable, and should I be worried? Whether CVE-2026-55079 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55079 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55079?
   • Upgrade github.com/coder/coder/v2 to 2.34.2 or later
   • Upgrade github.com/coder/coder/v2 to 2.33.8 or later
   • Upgrade github.com/coder/coder/v2 to 2.32.7 or later
   • Upgrade github.com/coder/coder/v2 to 2.29.17 or later

Other vulnerabilities in github.com/coder/coder/v2