PT-2026-51064 · Rubygems · Oj

Published

2026-06-19

·

Updated

2026-06-19

·

CVE-2026-54502

CVSS v4.0

8.7

High

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

Summary

Oj.dump is vulnerable to a stack-based buffer overflow when a large :indent value is provided by the developer. fill indent in dump.h calls memset(indent str, ' ', (size t)opts->indent) without validating the size. When opts->indent is set to INT MAX (2,147,483,647), the (size t) cast preserves the large value and memset writes 2 GB into the stack-allocated out buffer (4,184 bytes), corrupting the stack and crashing the process.

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 77:
c
static void fill indent(Out out, int depth) {
  if (0 < out->opts->indent) {
    size t len = (size t)(out->opts->indent * depth);
    // ...
    memset(out->buf + ..., ' ', len); // len = 2147483647 * depth
The indent option is accepted as a plain Ruby integer and stored as int without range validation. Multiplying by depth can produce a value larger than any stack or heap buffer.
ASAN report:
==69820==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fd1fc201278
WRITE of size 2147483647 at 0x7fd1fc201278 thread T0
  #0 memset
  #1 fill indent /ext/oj/dump.h:77
  #2 dump array  /ext/oj/dump compat.c:165
  #3 oj dump obj to json using params /ext/oj/dump.c:818
  #4 dump body  /ext/oj/oj.c:1429
  #5 dump     /ext/oj/oj.c:1480
Address is in stack of thread T0 at offset 4728 in frame:
  #0 dump /ext/oj/oj.c:1453
 [544, 4728) 'out' <== Memory access at offset 4728 overflows this variable

Reproduce

ruby
require "oj"
obj = [0]
Oj.dump(obj, mode: :compat, indent: 2 147 483 647)

Workaround

The develop should not use extreme indents and should not offer the option for users to dump Ruby data with unlimited indentation size.

Fix

Stack Overflow

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Weakness Enumeration

CWE-121

Related Identifiers

CVE-2026-54502
GHSA-3V45-F3VH-WG7M

Affected Products

Oj