CVE-2026-87029

undici vulnerable to Denial of Service via unhandled exception in the decompress interceptor

Workarounds

Avoid composing the decompress interceptor with a response handler that throws during response processing (such as dump with a maxSize) until upgrading.

undici's decompress interceptor forwards decompressed response data to the downstream handler from zlib stream event callbacks without catching exceptions those callbacks may throw. undici's engine converts a synchronous throw from a downstream handler into a per-request failure, but that protection is not in place when the throw happens asynchronously from a zlib callback. As a result, a downstream handler that throws by design, for example the built-in dump interceptor which throws when a response exceeds its maxSize, escapes as an uncaught exception and terminates the Node.js process.

A malicious or compromised HTTP server can crash any client that composes the decompress interceptor with dump (or another response handler that throws), by returning a small compressed body that decompresses to more than the configured limit. The compressed bytes on the wire are tiny, so only the decompressed size matters. If the application keeps the process alive with a global uncaught-exception handler, the affected request instead hangs until the body timeout.

CVE-2026-87029 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no 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 (7.30.1, 8.12.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to undici 7.30.1 or 8.12.2.

1. What is CVE-2026-87029? CVE-2026-87029 is a medium-severity security vulnerability in undici (npm), affecting versions >= 7.15.0, < 7.30.1. It is fixed in 7.30.1, 8.12.2.
2. How severe is CVE-2026-87029? CVE-2026-87029 has a CVSS score of 5.9 (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 undici are affected by CVE-2026-87029? undici (npm) versions >= 7.15.0, < 7.30.1 is affected.
4. Is there a fix for CVE-2026-87029? Yes. CVE-2026-87029 is fixed in 7.30.1, 8.12.2. Upgrade to this version or later.
5. Is CVE-2026-87029 exploitable, and should I be worried? Whether CVE-2026-87029 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-2026-87029 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-2026-87029?
   • Upgrade undici to 7.30.1 or later
   • Upgrade undici to 8.12.2 or later

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