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TI-2026-40063 Aliases CVE-2026-55517GHSA-x2qc-cmh9-f4hf

Deno: Denial of service via non-ASCII bytes in WebSocket response headers

Priority LOW 20CWE-248Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · Low
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-248.

Summary

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.5, a Deno program that opens a client WebSocket connection could be crashed by the remote server. While handling the WebSocket handshake response, Deno parsed the Sec-WebSocket-Protocol and Sec-WebSocket-Extensions response headers in a way that assumed their bytes were always printable ASCII. A response header containing non-visible-ASCII bytes (0x80-0xFF) caused a panic that aborted the entire Deno process. This vulnerability is fixed in 2.7.5.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00315 24th percentileScored 2026-11-07
Fix Fixed deno (denoland): 2.7.5deno (crates.io): 2.7.5

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
denolanddenobefore 2.7.52.7.5Patch availableCNA
—deno (crates.io)before 2.7.52.7.5Patch availableGHSA-x2qc-cmh9-f4hf
  • deno Vendordenoland Affected before 2.7.5 Fixed in 2.7.5 Patch available CNA
  • deno (crates.io) Vendor— Affected before 2.7.5 Fixed in 2.7.5 Patch available GHSA-x2qc-cmh9-f4hf

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:*before 2.7.5Vulnerabledenoland
  • cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:* Versions before 2.7.5 Vulnerable ·denoland

Remediation

  • Fix · CNA deno (denoland) Fixed in 2.7.5
  • Fix · GHSA-x2qc-cmh9-f4hf deno (crates.io) Fixed in 2.7.5 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55517
  2. 2026-10-03 Alias added: GHSA-x2qc-cmh9-f4hf

References

Advisory 1

Other 1

  • TI-2026-21627 Deno has a Command Injection via Incomplete shell metacharacter blocklist in node:child_process CVSS 3.1CRITICAL 9.8
  • TI-2025-17782 Deno's AES GCM authentication tags are not verified CVSS 4.0HIGH 7.7
  • TI-2024-18537 *const c_void / ExternalPointer unsoundness leading to use-after-free CVSS 3.1HIGH 8.8
  • TI-2024-18536 Deno arbitrary file descriptor close via `op_node_ipc_pipe()` leading to permission prompt bypass CVSS 3.1HIGH 8.8
  • TI-2023-12990 Deno is vulnerable to interactive `run` permission prompt spoofing via improper ANSI neutralization CVSS 3.1HIGH 8.8
  • TI-2023-11328 Regular expression denial of service in deno CVSS 3.1HIGH 7.5
See all 37 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences