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CVE-2026-54502

CVE-2026-54502 is a CWE-121 vulnerability in oj. O3 Security confirms whether CVE-2026-54502 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Oj: Stack Buffer Overflow in Oj.dump via Large Indent

Published
Jun 19, 2026
Updated
Jun 26, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Aug 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-54502.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk+0.08%
Lower risk than most CVEs26th percentile — riskier than 26% of all scored CVEsHighest risk
0.00%0.28%0.56%0.84%0.3%0.3%0.3%Jul 26Aug 26Aug 26

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected
💎oj

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

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:

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

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💎RubyGemsojall versions3.17.3

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for oj. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update oj to 3.17.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-54502 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether CVE-2026-54502 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-54502. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### 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)
O3 Security · Impact-Aware SCA

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