CVE-2026-54901 Oj: Use-After-Free in Oj::Parser array_class/hash_class GC Marking
A use-after-free vulnerability in the Oj Ruby gem allows attackers to cause a denial of service via a segmentation fault during JSON parsing.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54901?
CVE-2026-54901 is a medium-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, 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 in usual mode does not mark array_class and hash_class references during garbage collection, leading to Use-After-Free. If GC runs after the class is assigned but before a parse, the class object is reclaimed, leaving the parser holding a dangling VALUE. The subsequent parse call dereferences the freed object, producing a segfault. This issue has been fixed in version 3.17.2.
Weakness: CWE-416
Which versions are affected by CVE-2026-54901?
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-2026-54901?
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-2026-54901 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54901 exists.
Sources
Also known as DEBIAN-CVE-2026-54901, GHSA-vwm4-62gf-x745, MINI-2vrw-gg4m-4j67, MINI-3r87-4ccj-7m28, MINI-49gx-cfwj-7fjp, MINI-4jcw-qm4q-xfcf and 7 more.