Buffer overflow in Grunfink Snac2
CVE-2026-112021
snac2 before 2.93 contains a heap-based buffer overflow vulnerability in _xs_json_load_lexer() that allows unauthenticated remote attackers to corrupt heap memory by sending JSON strings containing a \u0000 escape. Attackers can send a single crafted application/activity+json POST to activitypub_post_handler(), which parses it before signature checks, overflowing heap allocations and crashing the server.
Vulnerability class: Buffer Overflow
Published .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- nullenvk.pl/posts/02-snac2-json (technical-description)
- gist.github.com/nullenvk/2bf288e2d34cb3d4b7143e61dbf7d90b (exploit)
- codeberg.org/grunfink/snac2/src/tag/2.92/xs_json.h (technical-description)
- codeberg.org/grunfink/snac2/commit/ec2c5c2046e0381bc942ec5d0d05ec861fe377e7 (patch)
- codeberg.org/grunfink/snac2/releases/tag/2.93 (release-notes)
- codeberg.org/grunfink/snac2 (product)
- www.vulncheck.com/advisories/snac2-before-2.93-heap-based-buffer-overflow-via-j… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-112021?
- CVE-2026-112021 is a high-severity vulnerability in Grunfink Snac2, classified under Heap-based Buffer Overflow. CVSS score: 7.5/10. Published 2026-10-18.
- How severe is CVE-2026-112021?
- High severity. CVSS v3 base score is 7.5 out of 10.