CVE-2026-21438
MEDIUMCVE-2026-21438 is a medium-severity (CVSS 5.3) CWE-401 vulnerability in github.com/quic-go/webtransport-go. O3 Security confirms whether CVE-2026-21438 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
webtransport-go affected by a Memory Exhaustion Attack due to Missing Cleanup of Streams Map
Blast Radius
github.com/quic-go/webtransport-goReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
webtransport-go is an implementation of the WebTransport protocol. Prior to 0.10.0, an attacker can cause unbounded memory consumption repeatedly creating and closing many WebTransport streams. Closed streams were not removed from an internal session map, preventing garbage collection of their resources. This vulnerability is fixed in v0.10.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/quic-go/webtransport-go | all versions | 0.10.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/quic-go/webtransport-go. 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 github.com/quic-go/webtransport-go to 0.10.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21438 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-2026-21438 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-2026-21438. 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-2026-21438 in your dependencies?
O3 detects CVE-2026-21438 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.