Resource exhaustion in Quic-Go Webtransport-Go
CVE-2026-21434
webtransport-go is an implementation of the WebTransport protocol. From 0.3.0 to 0.9.0, an attacker can cause excessive memory consumption in webtransport-go's session implementation by sending a WT_CLOSE_SESSION capsule containing an excessively large Application Error Message. The implementation does not enforce the draft-mandated limit of 1024 bytes on this field, allowing a peer to send an arbitrarily large message payload that is fully read and stored in memory. This allows an attacker to consume an arbitrary amount of memory. The attacker must transmit the full payload to achieve the memory consumption, but the lack of any upper bound makes large-scale attacks feasible given sufficient bandwidth. This vulnerability is fixed in 0.10.0.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.004 (34.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 34.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- Quic-Go Webtransport-Go — versions < 0.10.0
Weakness classification (CWE)
References
- github.com/quic-go/webtransport-go/security/advisories/GHSA-g6x7-jq8p-6q9q (Vendor Advisory)
- github.com/quic-go/webtransport-go/releases/tag/v0.10.0 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-21434?
- CVE-2026-21434 is a medium-severity vulnerability in Quic-Go Webtransport-Go, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.3/10. Published 2026-02-12.
- How severe is CVE-2026-21434?
- Medium severity. CVSS v3 base score is 5.3 out of 10.