Process crash via non-ASCII WebSocket response headers
Published Jun 23, 2026 · Updated Jun 23, 2026
Uncaught exception in Deno before 2.7.5 allows remote attackers to crash the process through a crafted WebSocket handshake response. The client-handshake parser calls HeaderValue::to_str() on Sec-WebSocket-Protocol and Sec-WebSocket-Extensions values without handling conversion errors for bytes outside visible ASCII. The victim application must initiate a connection to an attacker-controlled endpoint, or use plaintext ws:// where a man-in-the-middle attacker can alter the response; the effect is limited to terminating that Deno process.
Summary
What happened
Uncaught exception in Deno before 2.7.5 allows remote attackers to crash the process through a crafted WebSocket handshake response. The client-handshake parser calls HeaderValue::to_str() on Sec-WebSocket-Protocol and Sec-WebSocket-Extensions values without handling conversion errors for bytes outside visible ASCII. The victim application must initiate a connection to an attacker-controlled endpoint, or use plaintext ws:// where a man-in-the-middle attacker can alter the response; the effect is limited to terminating that Deno process.
The record
- CVE
- CVE-2026-55517
- Published
- Jun 23, 2026
- Updated
- Jun 23, 2026
- Vendor
- Deno Land Inc.
- Product
- Deno
- Classifications
- CWE-248, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 23, 2026CVE publishedPublication date reported by the CVE source.
- Jun 23, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 2.7.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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