CVE-2026-1528
HIGHCVE-2026-1528 is a high-severity (CVSS 7.5) CWE-248 vulnerability in undici. O3 Security confirms whether CVE-2026-1528 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
undici is vulnerable to Malicious WebSocket 64-bit length overflows undici parser and crashes the client
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
undicinpmDescription
ImpactA server can reply with a WebSocket frame using the 64-bit length form and an extremely large length. undici's ByteParser overflows internal math, ends up in an invalid state, and throws a fatal TypeError that terminates the process.
Patches
Patched in the undici version v7.24.0 and v6.24.0. Users should upgrade to this version or later.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | ≥ 6.0.0&&< 6.24.0 | 6.24.0 |
| 📦npm | undici | ≥ 7.0.0&&< 7.24.0 | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update undici to 6.24.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-1528 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 pinpoints whether CVE-2026-1528 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-1528. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-1528 in your dependencies?
O3 detects CVE-2026-1528 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.