CVE-2026-66731

facil.io 0.7.5 through 0.7.6 contains a denial-of-service vulnerability in the HTTP/1.1 chunked transfer encoding parser that allows unauthenticated remote attackers to crash the server by sending a negative chunk size value. Attackers can send a single POST request with a Transfer-Encoding: chunked header containing a leading minus sign in the chunk size field, causing the parser in http1_parser.h to compute a large positive integer from the negated value, corrupting internal state and moving the read pointer into unmapped memory resulting in a fault.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crash
https://tpaidakis.com/writeups/facilio-parser-dos/
https://www.vulncheck.com/advisories/facil-io-http-chunked-transfer-encoding-parser-crash-dos

Configurations

No configuration.

History

No history.

Information

Published : 2026-07-27 17:16

Updated : 2026-07-31 19:17

NVD link : CVE-2026-66731

Mitre link : CVE-2026-66731

CVE.ORG link : CVE-2026-66731

JSON object : View

Products Affected

No product.

CWE

CWE-125

Out-of-bounds Read

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