CVE-2026-9675: undici WebSocket client vulnerable to denial of service via cumulative fragment bypass

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

• nodejs undici8.0.0 and later · before 8.5.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (openjs). Independent of NVD's CPE analysis and usually ahead of it.

• undici undici

  • 8.5.0not affected
  • 8.0.0 and later · before 8.5.0affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2022-35949`undici.request` vulnerable to SSRF using absolute URL on `pathname`
  40Plan
• CVE-2026-1525undici is vulnerable to Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
  39Monitor
• CVE-2026-109829undici vulnerable to cache poisoning and cross-user disclosure via cross-origin redirects
  36Monitor

Published before and after this one in the same product

• ← EarlierCVE-2026-2581Mar 12, 2026 · undici is vulnerable to Unbounded Memory Consumption in in Undici's DeduplicationHandler via Response Buffering leads to DoS
  23Monitor
• ← EarlierCVE-2026-12151Jun 17, 2026 · undici WebSocket client vulnerable to denial of service via fragment count bypass
  30Monitor
• Later →CVE-2026-11525Jun 17, 2026 · undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching
  14Monitor

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1function expand(node) {2  return node.children.map(expand);3}

1const MAX_DEPTH = 32;2function expand(node, depth = 0) {3  if (depth > MAX_DEPTH) throw new Error("too deep");4  return node.children.map((c) => expand(c, depth + 1));5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.