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CVE-2026-55517— Deno: Denial of service via non-ASCII bytes in WebSocket response headers

Quick assessment

Affected
denoland deno
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Deno是Deno组织开源的一个简单、现代且安全的 JavaScript 和 TypeScript 运行环境。 Deno Land Deno 2.7.5之前版本存在异常处理不当漏洞，该漏洞源于处理WebSocket握手响应时对Sec-WebSocket-Protocol和Sec-WebSocket-Extensions标头的字节解析错误，假设其始终是可打印ASCII字符，包含非可见ASCII字节的响应标头可能导致整个Deno进程崩溃。

CVSS 4.3 · Medium EPSS 0.32% · P24

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
denoland deno < 2.7.5 affected
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I. Basic Information for CVE-2026-55517

Vulnerability Information
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Vulnerability Title
Deno: Denial of service via non-ASCII bytes in WebSocket response headers
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未捕获的异常
Source: CVE Program / CVE List V5
Vulnerability Title
Deno Land Deno 异常处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Deno是Deno组织开源的一个简单、现代且安全的 JavaScript 和 TypeScript 运行环境。 Deno Land Deno 2.7.5之前版本存在异常处理不当漏洞，该漏洞源于处理WebSocket握手响应时对Sec-WebSocket-Protocol和Sec-WebSocket-Extensions标头的字节解析错误，假设其始终是可打印ASCII字符，包含非可见ASCII字节的响应标头可能导致整个Deno进程崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
denoland deno < 2.7.5 -

II. Public POCs for CVE-2026-55517

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III. Intelligence Information for CVE-2026-55517

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Vendor Advisories for CVE-2026-55517 (1)

Same Patch Batch · denoland · 2026-06-23 · 10 CVEs total

CVE-2026-49402 8.1 HIGH Deno: Command Injection via spawnSync & spawn on Windows
CVE-2026-49440 7.4 HIGH Deno: Miller-Rabin Primality Test Allows Zero Rounds
CVE-2026-44726 7.4 HIGH Deno: TLS retry copies stale upgrade hook, risking plaintext traffic
CVE-2026-49401 7.3 HIGH Deno Permission Bypass via Unicode Normalization Mismatch on macOS (APFS)
CVE-2026-49411 6.5 MEDIUM Deno Node TCPWrap numeric hostname aliases bypass --deny-net resolved-IP deny checks
CVE-2026-49406 5.5 MEDIUM Deno: BYONM module resolution allows `package.json` main path traversal to bypass `--allow
CVE-2026-49983 5.2 MEDIUM Deno: process.loadEnvFile() bypasses env permission checks and mutates process.env with on
CVE-2026-49860 5.2 MEDIUM Deno: WebSocket API sandbox bypass via missing post-DNS check
CVE-2026-49859 5.2 MEDIUM Deno: `fetch()` API sandbox bypass via missing DNS resolution check

IV. Related Vulnerabilities

Same product: deno
Same vendor: denoland
Same weakness: CWE-248

V. Comments for CVE-2026-55517

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