CVE-2026-57497 is a medium-severity (CVSS 5.3) CWE-770 vulnerability in github.com/quic-go/webtransport-go. A fix is available for github.com/quic-go/webtransport-go — see the affected versions and patch details below.
webtransport-go: Memory Exhaustion Attack due to Buffering of Unknown Capsules
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-2026-57497.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-57497 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,308 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
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
Summary
An attacker can cause excessive memory allocation in webtransport-go by sending an unknown WebTransport capsule with a large payload. The implementation skips unknown capsules by reading the entire capsule body into memory, instead of draining it without retaining the data. This can lead to memory exhaustion.
Impact
A misbehaving or malicious peer can cause a denial-of-service (DoS) attack against webtransport-go clients or servers by triggering excessive memory allocation, potentially leading to crashes or resource exhaustion.
Details
WebTransport sessions use capsules on the HTTP/3 request stream. Unknown capsule types are ignored, but the capsule body still needs to be consumed before the next capsule can be parsed.
webtransport-go used io.ReadAll when skipping unknown capsules. Since the capsule reader is only limited by the capsule's declared length, a peer could send a large unknown capsule and cause the receiver to allocate memory for the full capsule body.
QUIC flow control limits buffered data, but it does not bound total allocation here, since reading the stream advances the flow control window while retaining the received bytes in memory.
The Fix
webtransport-go now drains unknown capsules to io.Discard instead of buffering them. This consumes the capsule body so parsing can continue, without retaining the payload in memory.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/quic-go/webtransport-go | all versions | 0.11.1go get github.com/quic-go/webtransport-go@v0.11.1 |
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/quic-go/webtransport-go to 0.11.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-57497 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.
Frequently Asked Questions
Is CVE-2026-57497 in your dependencies?
Find it across Go, including transitive dependencies.