# CVE-2026-54896: ohler55 Oj heap buffer overflow in Exception serialization

Source: https://junglewise.ai/threats/cve-2026-54896-ohler55-oj-heap-buffer-overflow-in-exception-serialization  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-01. Updated: 2026-07-01  
License: CC BY 4.0 with a link back

CVE-2026-54896 · Severity: high · CVSS 4 · Published 2026-07-01

Oj is a high-performance Ruby library used for processing and generating JSON data. A security flaw in the library's 'object mode' allows a heap buffer overflow to occur when generating JSON with extremely large indentation settings. While this typically requires a developer to manually set an unusually high indentation value, an exploit could lead to application crashes or memory corruption, potentially impacting service availability.

Technologies: [oj (RubyGems)](https://junglewise.ai/threats/technologies/oj). Vendors: [RubyGems](https://junglewise.ai/threats/vendors/rubygems).

## Quick answers

**Is CVE-2026-54896 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-54896 being exploited in the wild.

**How severe is CVE-2026-54896?** High severity, with a CVSS score of 4, published 1 July 2026.

**Which products and versions are affected?** oj (RubyGems) < 3.17.2, ECOSYSTEM:introduced=0,fixed=3.17.3.

**Is there a fix for CVE-2026-54896?** Yes. oj (RubyGems): upgrade to 3.17.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-54896 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-54896?** Check whether you run oj (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- oj (RubyGems): upgrade to 3.17.3 or later

  ```sh
  bundle update oj
  ```


## Technical details

A heap-based buffer overflow exists in the Oj Ruby gem's `Oj.dump` function when operating in `:object` mode. The vulnerability is located in `ext/oj/dump.h` within the `fill_indent` function, where the serializer fails to account for indentation bytes when calculating the required heap allocation for Exception objects. When a large `:indent` value (e.g., 5000) is provided, repeated calls to `memset` for indentation strings exceed the pre-allocated buffer, resulting in a write overflow. This issue requires the attacker to control the indentation parameter or for the application to use untrusted, extreme indentation settings. The flaw is addressed in version 3.17.2.

## Affected products

- ohler55 oj < 3.17.2

## Identifiers

- CVE-2026-54896
- GHSA-35w3-pjm6-wj95

## Timeline

- 2026-06-16: advisory: GitHub advisory published by maintainer
- 2026-06-30: disclosed: CVE published to NVD
- 2026-07-01: patched: Fix confirmed in version 3.17.2

## References

- [https://github.com/ohler55/oj/security/advisories/GHSA-35w3-pjm6-wj95](https://github.com/ohler55/oj/security/advisories/GHSA-35w3-pjm6-wj95)

## Related threats

- [ohler55 Oj integer overflow in Oj.load heap corruption](https://junglewise.ai/threats/cve-2026-54903-ohler55-oj-integer-overflow-in-oj-load-heap-corruption)
- [ohler55 Oj use-after-free in Oj::Parser SAJ mode](https://junglewise.ai/threats/cve-2026-54902-ohler55-oj-use-after-free-in-oj-parser-saj-mode)
- [ohler55 Oj Use-After-Free in Oj::Parser GC marking](https://junglewise.ai/threats/cve-2026-54901-ohler55-oj-use-after-free-in-oj-parser-gc-marking)
- [ohler55 Oj heap corruption in Oj::Parser via integer truncation](https://junglewise.ai/threats/cve-2026-54900-ohler55-oj-heap-corruption-in-oj-parser-via-integer-truncation)
- [ohler55 Oj heap use-after-free in Oj::Parser symbol_keys toggle](https://junglewise.ai/threats/cve-2026-54899-ohler55-oj-heap-use-after-free-in-oj-parser-symbol-keys-toggle)