CVE-2026-84890

undici vulnerable to Denial of Service via unbounded decompression of compressed responses

Workarounds

Once upgraded, set a conservative maxSize on the interceptor. Before upgrading, avoid using interceptors.decompress() with untrusted upstreams, or apply a custom interceptor that enforces a decompressed output size limit.

The interceptors.decompress() interceptor decompresses HTTP response bodies according to the untrusted Content-Encoding header. The number of decompression layers is capped at 5, but the total decompressed output size is not bounded and there is no option to limit it. A malicious or faulty upstream can return a small compressed payload (a compression bomb) that expands to hundreds of megabytes or gigabytes in client memory, exhausting memory and causing the Node.js process to crash or become unresponsive. Any application using the decompress interceptor to read responses from untrusted or compromised upstreams is affected.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-84890 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 (7.29.1, 8.10.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to 7.29.1 or 8.10.2. The interceptor now accepts a maxSize option (default 64 MiB) and rejects responses whose decompressed output exceeds it with a ResponseExceededMaxSizeError.

1. What is CVE-2026-84890? CVE-2026-84890 is a medium-severity allocation of resources without limits or throttling vulnerability in undici (npm), affecting versions >= 7.15.0, < 7.29.1. It is fixed in 7.29.1, 8.10.2. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2026-84890? CVE-2026-84890 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-2026-84890? undici (npm) versions >= 7.15.0, < 7.29.1 is affected.
4. Is there a fix for CVE-2026-84890? Yes. CVE-2026-84890 is fixed in 7.29.1, 8.10.2. Upgrade to this version or later.
5. Is CVE-2026-84890 exploitable, and should I be worried? Whether CVE-2026-84890 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-2026-84890 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-2026-84890?
   • Upgrade undici to 7.29.1 or later
   • Upgrade undici to 8.10.2 or later

Other vulnerabilities in undici