🛡️ CVE-2026-54899 — oj

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

Summary

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:

```c

// 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

```ruby

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

```