{"cve":"CVE-2026-21434","nvd":{"published":"2026-02-12T19:15:51.333","modified":"2026-06-17T10:18:39.907","status":"Analyzed","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_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-770"],"references":["https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0","https://github.com/quic-go/webtransport-go/security/advisories/GHSA-g6x7-jq8p-6q9q"],"products":["quic-go:webtransport-go"],"source":"nvd","synced_at":"2026-10-19T22:23:35.260773158+00:00"},"epss":{"cve":"CVE-2026-21434","score":0.00465,"percentile":0.40277,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-g6x7-jq8p-6q9q","url":"https://osv.dev/vulnerability/GHSA-g6x7-jq8p-6q9q","summary":"webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule","modified":"2026-09-10T03:50:35.012639183Z","packages":[{"ecosystem":"Go","name":"github.com/quic-go/webtransport-go","purl":"pkg:golang/github.com/quic-go/webtransport-go","ranges":[">=0.3.0 <0.10.0"],"fixed":["0.10.0"]}]},{"id":"GO-2026-4485","url":"https://osv.dev/vulnerability/GO-2026-4485","summary":"webtransport-go: Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule in github.com/quic-go/webtransport-go","modified":"2026-02-23T12:44:00.535972Z","packages":[{"ecosystem":"Go","name":"github.com/quic-go/webtransport-go","purl":"pkg:golang/github.com/quic-go/webtransport-go","ranges":["<0.10.0"],"fixed":["0.10.0"]},{"ecosystem":"Go","name":"github.com/marten-seemann/webtransport-go","purl":"pkg:golang/github.com/marten-seemann/webtransport-go","ranges":[">=0.3.0"],"fixed":[]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}