CVE-2026-1526 — undici
HIGHCVE-2026-1526 is a high-severity (CVSS 7.5) CWE-409 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
undici is vulnerable to Unbounded Memory Consumption in undici WebSocket permessage-deflate Decompression
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-1526.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-1526 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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.
undicinpmDescription
Description
The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive.
The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.
Impact
- Remote denial of service against any Node.js application using undici's WebSocket client
- A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more
- Memory exhaustion occurs in native/external memory, bypassing V8 heap limits
- No application-level mitigation is possible as decompression occurs before message delivery
Patches
Users should upgrade to fixed versions.
Workarounds
No workaround are possible.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | all versions | 6.24.0npm install undici@6.24.0 |
| 📦npm | undici | ≥ 7.0.0&&< 7.24.0 | 7.24.0npm install undici@7.24.0 |
Detection & mitigation playbook
Open-source dependencyDetect
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 6.24.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-1526 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-1526 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-1526. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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.
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-openshift-console-plugin-rhel9:4.2.0-9 | RHSA-2026:17789 |
| Red Hat Enterprise Linux 10 | nodejs22-1:22.22.2-1.el10_1 | RHSA-2026:7080 |
| Red Hat Enterprise Linux 10 | nodejs24-1:24.14.1-2.el10_1 | RHSA-2026:7675 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | nodejs22-1:22.22.2-2.el10_0 | RHSA-2026:7310 |
| Red Hat Enterprise Linux 8 | nodejs:22-8100020260331102257.6d880403 | RHSA-2026:7123 |
| Red Hat Enterprise Linux 8 | nodejs:24-8100020260408131901.6d880403 | RHSA-2026:7670 |
| Red Hat Enterprise Linux 9 | nodejs:22-9070020260401095228.rhel9 | RHSA-2026:7302 |
| Red Hat Enterprise Linux 9 | nodejs:24-9070020260402152654.rhel9 | RHSA-2026:7350 |
Frequently Asked Questions
Is CVE-2026-1526 in your dependencies?
O3 Security finds CVE-2026-1526 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.