# CVE-2026-21434: webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule

Source: https://junglewise.ai/threats/cve-2026-21434-webtransport-go-memory-exhaustion-attack-due-to-missing-length  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-19  
License: CC BY 4.0 with a link back

CVE-2026-21434 · Severity: low · CVSS 3.1 · Published 2026-02-19

webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule in github.com/quic-go/webtransport-go

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-2026-21434 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-21434 being exploited in the wild.

**How severe is CVE-2026-21434?** Low severity, with a CVSS score of 3.1, published 19 February 2026.

**Which products and versions are affected?** github.com/marten-seemann/webtransport-go (Go) SEMVER:introduced=0.3.0; github.com/quic-go/webtransport-go (Go) SEMVER:introduced=0,fixed=0.10.0, SEMVER:introduced=0.3.0,fixed=0.10.0.

**Is there a fix for CVE-2026-21434?** Yes. github.com/quic-go/webtransport-go (Go): upgrade to 0.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-21434?** Check whether you run github.com/marten-seemann/webtransport-go (Go) or github.com/quic-go/webtransport-go (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 0.10.0 or later

  ```sh
  go get github.com/quic-go/webtransport-go@v0.10.0
  ```


## Affected products

- github.com/marten-seemann/webtransport-go (Go) SEMVER:introduced=0.3.0
- github.com/quic-go/webtransport-go (Go) SEMVER:introduced=0,fixed=0.10.0, SEMVER:introduced=0.3.0,fixed=0.10.0

## Identifiers

- CVE-2026-21434
- GHSA-g6x7-jq8p-6q9q
- GO-2026-4485

## Related threats

- [quic-go webtransport-go memory exhaustion in capsule parsing](https://junglewise.ai/threats/cve-2026-57497-quic-go-webtransport-go-memory-exhaustion-in-capsule-parsing)
- [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)