{"document":{"category":"csaf_vex","csaf_version":"2.0","title":"CVE-2026-9675: undici WebSocket client vulnerable to denial of service via cumulative fragment bypass","publisher":{"category":"vendor","name":"HarborGuard Database","namespace":"https://database.harborguard.co"},"tracking":{"id":"CVE-2026-9675","status":"final","version":"1","initial_release_date":"2026-06-17T16:20:32.548Z","current_release_date":"2026-06-17T17:29:42.926Z","revision_history":[{"date":"2026-06-17T16:20:32.548Z","number":"1","summary":"Initial machine-readable export from HarborGuard."}]},"distribution":{"tlp":{"label":"WHITE"},"text":"Public CVE data; freely redistributable."},"notes":[{"category":"description","text":"Impact:\nThe undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.\n\nAffected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.\n\nThis is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.\n\nPatches:\nUpgrade to undici >= 8.5.0.\n\nWorkarounds:\nNo workaround is available. The fix must be applied through an upgrade.","title":"CVE description"}],"references":[{"category":"self","summary":"CVE-2026-9675 on HarborGuard Database","url":"https://database.harborguard.co/cve/CVE-2026-9675"},{"category":"external","summary":"CVE Record","url":"https://www.cve.org/CVERecord?id=CVE-2026-9675"},{"category":"external","summary":"github.com","url":"https://github.com/nodejs/undici/security/advisories/GHSA-38rv-x7px-6hhq"},{"category":"external","summary":"cna.openjsf.org","url":"https://cna.openjsf.org/security-advisories.html"}]},"product_tree":{"branches":[{"category":"vendor","name":"undici","branches":[{"category":"product_name","name":"undici","branches":[{"category":"product_version_range","name":">=8.0.0 <8.5.0","product":{"name":"undici undici >=8.0.0 <8.5.0","product_id":"CSAFPID-1","product_identification_helper":{"cpe":"cpe:2.3:a:undici:undici:*:*:*:*:*:*:*:*"}}},{"category":"product_version","name":"8.5.0","product":{"name":"undici undici 8.5.0","product_id":"CSAFPID-2","product_identification_helper":{"cpe":"cpe:2.3:a:undici:undici:*:*:*:*:*:*:*:*"}}}]}]}]},"vulnerabilities":[{"cve":"CVE-2026-9675","title":"undici WebSocket client vulnerable to denial of service via cumulative fragment bypass","notes":[{"category":"description","text":"Impact:\nThe undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.\n\nAffected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.\n\nThis is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.\n\nPatches:\nUpgrade to undici >= 8.5.0.\n\nWorkarounds:\nNo workaround is available. The fix must be applied through an upgrade.","title":"CVE description"}],"product_status":{"known_affected":["CSAFPID-1"],"fixed":["CSAFPID-2"]},"scores":[{"cvss_v3":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"products":["CSAFPID-1"]}],"remediations":[{"category":"vendor_fix","details":"Update to a fixed version: 8.5.0.","product_ids":["CSAFPID-1"]}]}]}