# CVE-2026-57497: quic-go webtransport-go memory exhaustion in capsule parsing

Source: https://junglewise.ai/threats/cve-2026-57497-quic-go-webtransport-go-memory-exhaustion-in-capsule-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-14. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-57497 · Severity: medium · CVSS 5.3 · Published 2026-09-14

webtransport-go is a Go library used to implement the WebTransport protocol, which allows for high-performance communication between web clients and servers. A vulnerability in how the library handles unrecognized data packets (capsules) allows a malicious user to force the application to consume excessive amounts of memory. This can lead to a denial-of-service (DoS) condition where the application crashes or becomes unresponsive, disrupting service for all users.

Technologies: [github.com/quic-go/webtransport-go (Go)](https://junglewise.ai/threats/technologies/github-com-quic-go-webtransport-go). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-57497 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-57497 being exploited in the wild.

**How severe is CVE-2026-57497?** Medium severity, with a CVSS score of 5.3, published 14 September 2026.

**Which products and versions are affected?** github.com/quic-go/webtransport-go (Go) <= 0.11.0, SEMVER:introduced=0,fixed=0.11.1; Quic-Go WebTransport-Go <= 0.11.0.

**Is there a fix for CVE-2026-57497?** Yes. github.com/quic-go/webtransport-go (Go): upgrade to 0.11.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-57497 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-57497?** Check whether you run github.com/quic-go/webtransport-go (Go) or Quic-Go WebTransport-Go at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/quic-go/webtransport-go (Go): upgrade to 0.11.1 or later

  ```sh
  go get github.com/quic-go/webtransport-go@v0.11.1
  ```


## Technical details

The vulnerability exists in the `Session.parseNextCapsule` function of webtransport-go. When the library encounters an unknown WebTransport capsule type on an HTTP/3 request stream, it attempts to skip it using `io.ReadAll`. Because the capsule reader is only limited by the length declared in the capsule header, a malicious peer can send a capsule with a massive payload, forcing the receiver to allocate a corresponding amount of memory. While QUIC flow control limits buffered data on the wire, it does not prevent this application-layer allocation because reading the stream advances the flow control window while the bytes are retained in memory. The issue is resolved in version 0.11.1 by using `io.Copy(io.Discard, r)` to drain unknown capsules without buffering them.

## Affected products

- quic-go webtransport-go <= 0.11.0

## Identifiers

- CVE-2026-57497
- GHSA-g35j-m5xg-vh3q
- GO-2026-6099

## Timeline

- 2026-06-20: other: Pull request to fix the issue submitted
- 2026-07-05: patched: Version 0.11.1 released
- 2026-07-24: advisory: GitHub Advisory published

## References

- [https://github.com/quic-go/webtransport-go/security/advisories/GHSA-g35j-m5xg-vh3q](https://github.com/quic-go/webtransport-go/security/advisories/GHSA-g35j-m5xg-vh3q)
- [https://github.com/quic-go/webtransport-go/pull/290](https://github.com/quic-go/webtransport-go/pull/290)
- [https://github.com/quic-go/webtransport-go/commit/3aecd11736579530ff067651c30a543eb0b4b8c4](https://github.com/quic-go/webtransport-go/commit/3aecd11736579530ff067651c30a543eb0b4b8c4)
- [https://github.com/quic-go/webtransport-go/releases/tag/v0.11.1](https://github.com/quic-go/webtransport-go/releases/tag/v0.11.1)
- [https://api.github.com/repos/quic-go/webtransport-go/security-advisories/GHSA-g35j-m5xg-vh3q](https://api.github.com/repos/quic-go/webtransport-go/security-advisories/GHSA-g35j-m5xg-vh3q)

## Related threats

- [webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule](https://junglewise.ai/threats/cve-2026-21434-webtransport-go-memory-exhaustion-attack-due-to-missing-length)
- [GO-2026-4488 - webtransport-go: CloseWithError can block indefinitely in github.com/quic-go/webtransport-go](https://junglewise.ai/threats/cve-2026-21435-webtransport-go-closewitherror-can-block-indefinitely)
- [webtransport-go: Memory Exhaustion Attack due to Missing Cleanup of Streams Map](https://junglewise.ai/threats/cve-2026-21438-webtransport-go-memory-exhaustion-attack-due-to-missing-cleanup)