CVE-2026-55517: CWE-248: Uncaught Exception in denoland deno
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.
AI Analysis
Technical Summary
CVE-2026-55517 affects Deno, a JavaScript, TypeScript, and WebAssembly runtime. The vulnerability arises during the handling of WebSocket handshake responses, specifically when parsing the Sec-WebSocket-Protocol and Sec-WebSocket-Extensions headers. The code incorrectly assumes these headers contain only printable ASCII bytes. If a response header includes bytes in the range 0x80-0xFF (non-visible ASCII), this triggers a panic that aborts the entire Deno process. This denial-of-service condition can be triggered by a remote server. The vulnerability is resolved in Deno version 2.7.5.
Potential Impact
An attacker controlling a remote WebSocket server can cause a denial-of-service by crashing the Deno client process during the WebSocket handshake. There is no impact on confidentiality or integrity, only availability is affected.
Mitigation Recommendations
A fix is available in Deno version 2.7.5. Users should upgrade to version 2.7.5 or later to remediate this vulnerability. No other mitigations are indicated.
CVE-2026-55517: CWE-248: Uncaught Exception in denoland deno
Description
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.
CVSS v3.1
Score 4.3medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-55517 affects Deno, a JavaScript, TypeScript, and WebAssembly runtime. The vulnerability arises during the handling of WebSocket handshake responses, specifically when parsing the Sec-WebSocket-Protocol and Sec-WebSocket-Extensions headers. The code incorrectly assumes these headers contain only printable ASCII bytes. If a response header includes bytes in the range 0x80-0xFF (non-visible ASCII), this triggers a panic that aborts the entire Deno process. This denial-of-service condition can be triggered by a remote server. The vulnerability is resolved in Deno version 2.7.5.
Potential Impact
An attacker controlling a remote WebSocket server can cause a denial-of-service by crashing the Deno client process during the WebSocket handshake. There is no impact on confidentiality or integrity, only availability is affected.
Mitigation Recommendations
A fix is available in Deno version 2.7.5. Users should upgrade to version 2.7.5 or later to remediate this vulnerability. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-16T22:44:22.284Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a3ac4f0eed863c81e618259
Added to database: 06/23/2026, 17:40:00 UTC
Last enriched: 06/23/2026, 17:54:43 UTC
Last updated: 06/23/2026, 18:09:40 UTC
Views: 3
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