CVE-2026-54902: Oj: Use-After-Free in Oj::Parser SAJ Long Key Callback

Severity: medium (CVSS 6.3 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-01 · updated 2026-10-25
Weakness: CWE-416

Description

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. Prior to version 3.17.2, is vulnerable to Use-After-Free when in SAJ mode. The Oj::Parser does not protect cached object keys (≥ 35 bytes) from garbage collection, and a Ruby callback that triggers GC inside hash_end can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address 0x4242 (a canary-style pattern suggesting control over the freed memory's content). This issue has been fixed in version 3.17.2.

Affected products

Rubygems Oj: before 3.17.3; 0.5, 0.5.1, 0.5.2, 0.6.0, 0.7.0, 0.8.0 (+288) — fixed in 3.17.3
ohler55 oj: before 3.17.2

How to fix

Upgrade to a fixed version: Rubygems Oj 3.17.3. Check the vendor advisory for mitigations.

References

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