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 s
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.
Details
Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-66731
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-667310.47% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 38% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-66731 | coverage & exploitation status | NVD · CVE.org |
Recent advisories for facil.io
A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.
- highCVE-2026-66730: facil.io 0.6.0 through 0.7.6 contains a denial-of-service vulnerability in the multipart body …nvd · 2026-07-27
- highCVE-2026-66729: facil.io 0.6.0 through 0.7.6 contains an integer underflow vulnerability in the multipart MIME…nvd · 2026-07-27
- mediumCVE-2026-16653: A security flaw has been discovered in boazsegev facil.io up to 0.7.58. This affects the funct…nvd · 2026-07-23
- highCVE-2026-16632: A flaw has been found in boazsegev facil.io up to 0.7.4. Affected is the function websocket_on…nvd · 2026-07-23
More from NVD Recent CVEs
- mediumCVE-2026-67355: guzzlehttp/guzzle versions before 7.15.1 fail to preserve host-only cookie scope, storing the …2026-08-01
- mediumCVE-2026-67354: guzzlehttp/guzzle versions before 7.15.1 contain an information disclosure vulnerability in Re…2026-08-01
- mediumCVE-2026-67353: guzzlehttp/guzzle versions before 7.15.1 contain a denial of service vulnerability in the Cook…2026-08-01
- highCVE-2026-67352: luci-app-https-dns-proxy contains a stored cross-site scripting vulnerability in the resolver_…2026-08-01
- mediumCVE-2026-67344: ArcadeDB before 26.7.2 fails to enforce the UPDATE_SCHEMA database permission on the ALTER TYP…2026-08-01