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{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:quic-go:webtransport-go:*:*:*:*:*:go:*:*", "matchCriteriaId": "D64C55F6-7FB5-4D98-9E14-99F89DD9F3E4", "versionEndExcluding": "0.10.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "webtransport-go is an implementation of the WebTransport protocol. Prior to v0.10.0, an attacker can cause a denial of service in webtransport-go by preventing or indefinitely delaying WebTransport session closure. A malicious peer can withhold QUIC flow control credit on the CONNECT stream, blocking transmission of the WT_CLOSE_SESSION capsule and causing the close operation to hang. This vulnerability is fixed in v0.10.0."}], "id": "CVE-2026-21435", "lastModified": "2026-02-19T22:51:49.417", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 1.4, "source": "security-advisories@github.com", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "nvd@nist.gov", "type": "Primary"}]}, "published": "2026-02-12T19:15:51.503", "references": [{"source": "security-advisories@github.com", "tags": ["Product", "Release Notes"], "url": "https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0"}, {"source": "security-advisories@github.com", "tags": ["Vendor Advisory"], "url": "https://github.com/quic-go/webtransport-go/security/advisories/GHSA-px4r-g4p3-hhqv"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-400"}], "source": "security-advisories@github.com", "type": "Primary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,0.10.0)"}}], "product": "webtransport-go", "vendor": "quic-go"}], "analysis": {"en": {"generated_at": "2026-04-17T20:03:38.860521+00:00", "value": {"mitigation_remediation": ["Upgrade webtransport-go to version 0.10.0 or later.", "If an upgrade is not immediately possible, monitor sessions for failed closure and enforce a timeout or reset connections after a defined period.", "Validate peer behavior and consider rejecting connections that exhibit abnormal flow control handling."], "summary": {"action": "Patch Now", "impact": "Denial of Service"}, "threat_synthesis": {"affected_systems": "The vulnerability affects quic-go\u2019s webtransport-go library. All versions prior to 0.10.0 are vulnerable; the fix is included in v0.10.0 and later releases.", "description_and_impact": "webtransport-go implements the WebTransport protocol and contains a flaw that lets an attacker cause a denial of service by preventing or indefinitely delaying the closure of a WebTransport session. The attacker can hold back QUIC flow control credit on the CONNECT stream, blocking transmission of the WT_CLOSE_SESSION capsule and causing the close operation to hang. The effect is a stuck connection that cannot be terminated normally.", "risk_and_exploitability": "The CVSS score of 5.3 indicates moderate severity, while the EPSS score of <1% signals a very low likelihood of exploitation. The flaw is not listed in the CISA KEV catalog. Attackers must control a malicious peer capable of withholding QUIC flow control credit on the CONNECT stream; successful exploitation results in a session that remains open indefinitely, leading to a denial of service for the affected application."}}}}, "created": "2026-02-13T21:35:24.782848+00:00", "updated": "2026-04-17T20:15:26.991297+00:00", "vendors": ["quic-go", "quic-go$PRODUCT$webtransport-go"]}