CVE-2026-54899: Oj: Use-After-Free in Oj::Parser Symbol Key Cache Toggle

Severity: medium (CVSS 6.3 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% 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, disabling symbol_keys on a reused Oj::Parser instance triggers a heap use-after-free. When symbol_keys is toggled from true to false, opt_symbol_keys_set frees the internal key cache (cache_free) but does not clear the pointer. The next parse call reads from the freed cache via cache_intern, producing a use-after-free. This issue has been fixed in version 3.17.2.

Affected products

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

How to fix

Upgrade to a fixed version: Rubygems Oj 3.17.2. Check the vendor advisory for mitigations.

References

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