CVE-2026-66731 | facil.io 0.7.5 through 0.7.6 contains a denial-of-service vu… | CVSS 7.5 HIGH

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.

Metadata

CVE ID: CVE-2026-66731
State: PUBLISHED
Assigner: VulnCheck
Reserved: 2026-07-27 16:27 UTC
Published: 2026-07-27 16:57 UTC
Last updated: 2026-07-27 17:30 UTC
Primary CWE: CWE-125
Out-of-bounds Read
Vendor / Product: boazsegev / facil.io
Sources: cve.org · NVD

Severity & Metrics

7.5 HIGH CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC — CISA Coordinator

Exploitation: PoC
Automatable: yes
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
boazsegev	facil.io	—	0.7.5 ≤ 0.7.6

Weakness (CWE)

CWE	Source	Description
CWE-125	cna	Out-of-bounds Read

CVSS scores (2)

Score	Severity	Version	Source	Vector
8.7	HIGH	4.0	cna	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5	HIGH	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References (2)