CVE-2026-21434
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.43%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.43% probability · 36th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-770
- Affected
- quic-go/webtransport-go
- Source
- security-advisories@github.com
References
- https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0Product, Release Notes
- https://github.com/quic-go/webtransport-go/security/advisories/GHSA-g6x7-jq8p-6q9qVendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.