CVE-2026-66729 facil.io 0.6.0 - 0.7.6 Integer Underflow DoS via Multipart MIME Body Parser
Remote attackers can crash the server via integer underflow in the multipart MIME parser, requiring an upgrade to facil.io.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-66729?
CVE-2026-66729 is a high-severity vulnerability in boazsegev facil.io, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-125
Which versions are affected by CVE-2026-66729?
How do I fix CVE-2026-66729?
No fix has been published for CVE-2026-66729 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-66729 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66729 exists.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-g2qx-6r8w-37px.