CVE-2026-41146

facil.io is a C micro-framework for web applications. Prior to commit 5128747363055201d3ecf0e29bf0a961703c9fa0, `fio_json_parse` can enter an infinite loop when it encounters a nested JSON value starting with `i` or `I`. The process spins in user space and pegs one CPU core at ~100% instead of returning a parse error. Because `iodine` vendors the same parser code, the issue also affects `iodine` when it parses attacker-controlled JSON. The smallest reproducer I found is `[i`. The quoted-value form that originally exposed the issue, `[""i`, reaches the same bug because the parser tolerates missing commas and then treats the trailing `i` as the start of another value. Commit 5128747363055201d3ecf0e29bf0a961703c9fa0 fixes the issue.

CVSS 4.0

8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

EPSS

0.3% chance of exploitation in the next 30 days; higher than 21% of CVEs (scores of 2026-10-26)

CWEs

CWE-400, CWE-835

Published

2026-04-22

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Packages (OSV)

References

• https://github.com/boazsegev/facil.io/commit/5128747363055201d3ecf0e29bf0a961703c9fa0
• https://github.com/boazsegev/facil.io/security/advisories/GHSA-2x79-gwq3-vxxm
• https://github.com/boazsegev/facil.io/security/advisories/GHSA-2x79-gwq3-vxxm

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