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:

// 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