facil.io 0.7.5 - 0.7.6 HTTP/1.1 Chunked Transfer Encoding Parser Crash DoS
41Vexday Risk Score
No sign of exploitation. It has a public proof of concept.
ssvc Attendcvss 8.7epss 0.5%
from disclosure to weapon0 days
Published on NVDJul 27
1st PoCJul 24
exploitation probability
0.5%top 62% of all CVEs
observed exploitation
nono source reports it
2 public exploit(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.
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
Affected products
boazsegev · facil.iopublic PoCs found — 2
githubgithub.com/theopaid/CVE-2026-66731-Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-leading-to-Server-Crash★ 0cve_referencegithub.com/theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crashunverified⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.