CVE-2026-54896: Oj Heap Buffer Overflow Vulnerability

HIGH
Advisory Identifier: GHSA-35w3-pjm6-wj95
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CWE-122
Published
Advisory Summary

CVE-2026-54896 is a HIGH heap buffer overflow vulnerability (CWE-122: Heap-based Buffer Overflow) affecting Oj libraries in the RubyGems ecosystem. The issue involves heap buffer overflow in oj.dump exception serialization via large indent. Remediation is available by upgrading affected packages to version 3.17.3.

CVE-2026-54896 at a Glance

CVE Identifier CVE-2026-54896
GHSA Identifier GHSA-35w3-pjm6-wj95
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-122: Heap-based Buffer Overflow
Affected Product Oj
Package Ecosystem RubyGems
Published Date
Last Updated

How to Fix CVE-2026-54896

To remediate this vulnerability, upgrade all affected Oj dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

oj fixed: 3.17.3 
Upgrade oj to 3.17.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for oj

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-54896, inspect your project dependencies for Oj:

inspect dependencies for oj

Analyze the terminal output to locate any version of Oj in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.17.3), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-122: Heap-based Buffer Overflow, where a heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). In Oj, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2026-54896 Affected Oj Versions

1 component(s)
Fixed Versions:
3.17.3
Product / Package Ecosystem Affected Versions Fixed Version
oj
gem/oj
RubyGems
< 3.17.3
3.17.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/ohler55/oj/security/advisories/GHSA-35w3-pjm6-wj95
Oj Source Repository REPOSITORY
https://github.com/ohler55/oj

Frequently Asked Questions

What is CVE-2026-54896?
CVE-2026-54896 is a security vulnerability in Oj involving Heap Buffer Overflow in Oj.dump Exception Serialization via Large Indent under CWE-122: Heap-based Buffer Overflow.
Which Oj versions are affected?
Affected versions include releases prior to 3.17.3 across affected packages: oj.
What version fixes CVE-2026-54896?
Upgrading to 3.17.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is oj affected?
Yes, oj is affected in releases prior to 3.17.3. Upgrade your dependency to 3.17.3 or later.
What CWE is associated with CVE-2026-54896?
CVE-2026-54896 is classified under CWE-122: Heap-based Buffer Overflow (A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().).
How can I check RubyGems dependencies for CVE-2026-54896?
Run the dependency tree command: 'inspect dependencies for oj'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-35w3-pjm6-wj95",
  "modified" : "2026-06-19T19:36:47Z",
  "published" : "2026-06-19T19:36:47Z",
  "aliases" : [ "CVE-2026-54896" ],
  "summary" : "Oj: Heap Buffer Overflow in Oj.dump Exception Serialization via Large Indent",
  "details" : "### Summary\n\n`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.\n\n### Version\n\n- **Software**: oj gem\n- **Affected**: all versions with `ext/oj/dump.h`\n- **Latest tested**: 3.17.1 (confirmed present)\n\n### Details\n\n`ext/oj/dump.h`, line 75–77:\n\n```c\nstatic void fill_indent(Out out, int depth) {\n    if (0 < out->opts->indent) {\n        memset(out->buf + out->cur, ' ', (size_t)(out->opts->indent * depth));\n```\n\nWhen 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.\n\nASAN report:\n```\n==101656==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x527000022c5e\nWRITE of size 5000 at 0x527000022c5e thread T0\n    #0 memset\n    #1 fill_indent       /ext/oj/dump.h:77\n    #2 dump_obj_attrs    /ext/oj/dump_object.c:552\n    #3 dump_obj          /ext/oj/dump_object.c:80\n    #4 oj_dump_obj_val   /ext/oj/dump_object.c:708\n    #5 oj_dump_obj_to_json_using_params  /ext/oj/dump.c:817\n    #6 dump_body         /ext/oj/oj.c:1429\n    #7 dump              /ext/oj/oj.c:1480\n0x527000022c5e is located 0 bytes after 13150-byte region [0x52700001f900, 0x527000022c5e)\n```\n\n### Reproduce\n\n```ruby\nrequire \"oj\"\nobj = Oj.load('{\"^o\":\"RuntimeError\"}', mode: :object)\nOj.dump(obj, mode: :object, indent: 5000)\n```\n\n### Workarounds\n\nThis 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "oj"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.17.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 3.17.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ohler55/oj/security/advisories/GHSA-35w3-pjm6-wj95"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ohler55/oj"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-122" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T19:36:47Z",
    "nvd_published_at" : null
  }
}