Описание
Oj: Use-After-Free in Oj::Parser SAJ Long Key Callback
Summary
Oj::Parser in SAJ mode does not protect cached object keys (≥ 35 bytes) from garbage collection. 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).
Version
- Software: oj gem
- Affected: all versions with
ext/oj/saj2.c/ext/oj/parser.c - Latest tested: 3.17.1 (confirmed present)
Details
Short keys (≤ 34 bytes) are stored inline on the C stack and are safe. Long keys (≥ 35 bytes) are stored as heap-allocated Ruby String objects passed to rb_funcall as the key argument. Between the key being resolved and the callback completing, a GC triggered inside the callback (e.g. GC.start) can collect the key String, leaving a dangling VALUE.
Crash output:
The freed VALUE 0x4242 shows the attacker-controlled content of the key string was loaded as a pointer — a classic use-after-free indicator.
Reproduce
Пакеты
oj
< 3.17.2
3.17.3
Связанные уязвимости
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.
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.
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.
Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as ...