CVE-2026-66731 Details
Description
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.
A denial-of-service vulnerability has been identified in facil.io versions 0.7.5 through 0.7.6. The issue arises in the HTTP/1.1 chunked transfer encoding parser, where the parser incorrectly handles negative chunk size values. This flaw allows unauthenticated remote attackers to crash the server by sending a POST request with a Transfer-Encoding: chunked header that includes a leading minus sign in the chunk size field. The parser, located in http1_parser.h, converts the negative value into a large positive integer, corrupting the internal state. This corruption moves the read pointer into unmapped memory, causing a fault and crashing the server.
Users can update to facil.io version 0.7.7 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jul 27, 2026CISA-ADP
Assessed Jul 27, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-125 | Out-of-bounds Read | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| facil.io | >= 0.7.5, <= 0.7.6 (semver) |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 31, 2026 | CVE Modified | [email protected] |
| Jul 27, 2026 | CVE Modified | CISA-ADP |
| Jul 27, 2026 | New CVE Received | [email protected] |