Summary
Oj: Use-After-Free in Oj::Parser Symbol Key Cache Toggle
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.
Version
- Software: oj gem
- Affected: all versions with
ext/oj/usual.c - Latest tested: 3.17.1 (confirmed present)
Details
ext/oj/usual.c, opt_symbol_keys_set:
// usual.c:1043–1051
if (symbol_keys) {
d->key_cache = cache_create(...); // allocate
} else {
cache_free(d->key_cache); // free, but d->key_cache pointer not NULLed
}
On the next parse call, cache_key → cache_intern reads from d->key_cache which now points to freed memory.
ASAN report:
==145265==ERROR: AddressSanitizer: heap-use-after-free on address 0x50b00001a318
READ of size 8 at 0x50b00001a318 thread T0
#0 cache_intern /ext/oj/cache.c:328
#1 cache_key /ext/oj/usual.c:161
#2 close_object /ext/oj/usual.c:285
#3 parse /ext/oj/parser.c:693
#4 parser_parse /ext/oj/parser.c:1408
freed by thread T0 here:
#0 free
#1 cache_free /ext/oj/cache.c:277
#2 opt_symbol_keys_set /ext/oj/usual.c:1051
#3 option /ext/oj/usual.c:1111
#4 parser_missing /ext/oj/parser.c:1362
0x50b00001a318 is 40 bytes inside freed 112-byte region [fd]fd fd fd fd fd fd fd
Reproduce
require 'oj'
p = Oj::Parser.new(:usual, symbol_keys: true)
p.symbol_keys = false # frees cache without nulling pointer
p.parse('{"attacker":1}') # UAF: reads freed cache
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-54899? CVE-2026-54899 is a high-severity use after free vulnerability in oj (rubygems), affecting versions < 3.17.2. It is fixed in 3.17.3. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- Which versions of oj are affected by CVE-2026-54899? oj (rubygems) versions < 3.17.2 is affected.
- Is there a fix for CVE-2026-54899? Yes. CVE-2026-54899 is fixed in 3.17.3. Upgrade to this version or later.
- Is CVE-2026-54899 exploitable, and should I be worried? Whether CVE-2026-54899 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-54899 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-54899? Upgrade
ojto 3.17.3 or later.