How severe is CVE-2026-84890?

CVE-2026-84890 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-84890?

CVE-2026-84890 affects the following packages: undici (npm), undici (npm). Ecosystems affected: npm.

How do I fix CVE-2026-84890?

Update undici to 7.29.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84890 is resolved across your whole dependency graph.

How do I detect CVE-2026-84890 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-84890 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-84890 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-84890 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-84890?

CVE-2026-84890 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 34th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-84890?

CVE-2026-84890 is classified as CWE-770 (CWE-770). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-84890 published, and has it been updated?

CVE-2026-84890 was published on September 4, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

CVE-2026-84890 — undici

MEDIUMFix: nodejs/undici@2c7d7e1

CVE-2026-84890 is a medium-severity (CVSS 5.9) CWE-770 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.

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

Also known asGHSA-3xpg-4rpp-hhhm

Published

Sep 4, 2026

Updated

Oct 21, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-84890.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-84890 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

9Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

undicinpm

143.8Mdownloads / week

Description

Impact

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.

Patches

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.

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.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`undici`	≥ 7.15.0&&< 7.29.1	7.29.1`npm install undici@7.29.1`
📦npm	`undici`	≥ 8.0.0&&< 8.10.2	8.10.2`npm install undici@8.10.2`

Affected Products

1 product · 2 configurations

Application

undicinodejs

≥ 8.0.0 && < 8.10.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 7.29.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84890 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

The undici library, used in some Red Hat products, is vulnerable to a denial of service. This occurs when processing untrusted compressed HTTP responses, which can lead to unbounded memory consumption and application crashes. The Moderate severity is due to the requirement of a malicious or faulty upstream server to…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-84890 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Hardened Images	`nodejs26-main-11.19.0-1.26.7.0.1.5.2.hum1`	RHSA-2026:54389
Red Hat Hardened Images	`nodejs24-main-11.16.0-1.24.18.1.0.2.2.hum1`	RHSA-2026:54438
Red Hat Hardened Images	`grafana12-4-main-12.4.10-0.2.hum1`	RHSA-2026:66008

Frequently Asked Questions

### Impact 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 u