CVE-2026-54898 Oj: Use-After-Free in Oj::Parser SAJ Callback via Input Mutation
A use-after-free vulnerability in the Oj Ruby gem allows attackers to execute arbitrary code or cause denial of service via crafted JSON input.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54898?
CVE-2026-54898 is a low-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.2,Oj::Parser#parse is vulnerable to a heap use-after-free when a SAJ/SAJ2 callback mutates the input JSON string during parsing. The C engine holds a raw const byte * pointer into the Ruby string's internal buffer. If a callback (e.g. hash_start) resizes the string — for example by calling String#replace with a longer value — Ruby reallocates the string buffer and frees the old one. The C parser's pointer is left dangling; the next character read at parser.c:607 is a use-after-free. This issue has been fixed in version 3.17.2.
Weakness: CWE-416
Which versions are affected by CVE-2026-54898?
2 open source packages ship an affected version, including oj.
| Package | Affected | Fixed in |
|---|---|---|
oj RubyGems | All versions | 3.17.3 |
oj RubyGems | All versions | 3.17.3 |
How do I fix CVE-2026-54898?
Upgrade oj to 3.17.3 or later.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-54898 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54898 exists.
Sources
Also known as DEBIAN-CVE-2026-54898, GHSA-q2gm-54r6-8fwm, MINI-3832-5v48-3724, MINI-82hq-3wfg-ww4q, MINI-8m6f-r894-q979, MINI-9v4w-m9qp-gj88 and 7 more.