Vulnerability · Published Jul 27, 2026 · Assigned by VulnCheck

CVE-2026-66729facil.io 0.6.0 - 0.7.6 Integer Underflow DoS via Multipart MIME Body Parser

High 7.5

In plain English

A high-severity out-of-bounds read in facil.io from boazsegev. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 56% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.8%top 43.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack tooling1Public PoC

Official description

facil.io 0.6.0 through 0.7.6 contains an integer underflow vulnerability in the multipart MIME body parser that allows unauthenticated remote attackers to crash the server process by sending a crafted Content-Disposition header with an empty field name. Attackers can trigger a uint32_t wraparound in http_mime_parser.h causing an out-of-bounds memory read past the name pointer, resulting in a bus fault that crashes the handling worker with a single POST request.

Affected products (as reported)

Vendor	Product	Versions
boazsegev	facil.io	0.6.0 – through 0.7.6

Weakness: CWE-125 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Researcher Blog technical-description, exploit
Researcher Disclosure technical-description, exploit
https://www.vulncheck.com/advisories/facil-io-integer-underflow-dos-via-multipart-mime-body-parser third-party-advisory