CVE-2026-66731: high-severity vulnerability in boazsegev facil.io
facil.io 0.7.5 - 0.7.6 HTTP/1.1 Chunked Transfer Encoding Parser Crash DoS
Published · Updated
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41Vexday Risk Score
No sign of exploitation. It has a public proof of concept.
ssvc Attendcvss 8.7epss 0.8%
from disclosure to weaponsame day
Published on NVDJul 27
1st PoCJul 24
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 — 3
githubgithub.com/theopaid/CVE-2026-66731-Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-leading-to-Server-Crash★ 0cve_referencetpaidakis.com/writeups/facilio-parser-dos/unverifiedcve_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.
Related CVEs — boazsegev facil.io
In the same product, most dangerous first.
CVE-2026-66730HIGHfacil.io 0.6.0 - 0.7.6 Infinite Loop DoS via Multipart MIME Body ParserEPSS 0.8%CVE-2026-66729HIGHfacil.io 0.6.0 - 0.7.6 Integer Underflow DoS via Multipart MIME Body ParserEPSS 0.8%CVE-2026-16653MEDIUMboazsegev facil.io Public Folder http.c http_sendfile2 path traversalEPSS 0.7%CVE-2026-16632MEDIUMboazsegev facil.io WebSocket Frame websocket_parser.h websocket_on_protocol_error input validationEPSS 0.5%CVE-2026-41146HIGHfacil.io and downstream iodine ruby gem vulnerable to uncontrolled resource consumption and loop with unreachable exit conditionEPSS 0.4%