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.
References7
- codeberg.org/grunfink/snac2
- codeberg.org/grunfink/snac2/commit/ec2c5c2046e0381bc942ec5d0d05…
- codeberg.org/grunfink/snac2/releases/tag/2.93
- codeberg.org/grunfink/snac2/src/tag/2.92/xs_json.h#L283-L285
- gist.github.com/nullenvk/2bf288e2d34cb3d4b7143e61dbf7d90b
- nullenvk.pl/posts/02-snac2-json
- www.vulncheck.com/advisories/snac2-before-2.93-heap-based-buffe…
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 4.0
-
8.7
HIGH
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 52 · as of 10 November 2026
- CWE
- CWE-122
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.