Vulnerability · Published Oct 18, 2026 · Assigned by VulnCheck
CVE-2026-112021snac2 before 2.93 Heap-Based Buffer Overflow via JSON Parser _xs_json_load_lexer()
High 7.5
In plain English
A high-severity heap buffer overflow in snac2 from grunfink. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 52% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | snac2 | no fix listed | DEBIAN-CVE-2026-112021 |
| Debian:14 | snac2 | 2.93-1 | DEBIAN-CVE-2026-112021 |
| Ubuntu:24.04:LTS | snac2 | no fix listed | UBUNTU-CVE-2026-112021 |
| Ubuntu:26.04:LTS | snac2 | no fix listed | UBUNTU-CVE-2026-112021 |
Affected products (as reported)
Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://nullenvk.pl/posts/02-snac2-json technical-description
- https://gist.github.com/nullenvk/2bf288e2d34cb3d4b7143e61dbf7d90b exploit
- https://codeberg.org/grunfink/snac2/src/tag/2.92/xs_json.h#L283-L285 technical-description
- https://codeberg.org/grunfink/snac2/commit/ec2c5c2046e0381bc942ec5d0d05ec861fe377e7 patch
- https://codeberg.org/grunfink/snac2/releases/tag/2.93 release-notes
- https://codeberg.org/grunfink/snac2 product
- VulnCheck Advisory: snac2 before 2.93 Heap-Based Buffer Overflow via JSON Parser _xs_json_load_lexer() third-party-advisory