Summary
Oj: Integer Overflow in Oj.load 2GB String Handling
Oj.load is vulnerable to heap corruption when parsing a JSON string longer than 2 GB. An integer overflow in buf_append_string (buf.h:61) converts the string length to a large negative size_t, causing memcpy to copy an astronomically large amount of data out of bounds. This crashes the process and can corrupt adjacent heap memory.
Version
- Software: oj gem
- Affected: all versions with
ext/oj/buf.handext/oj/parse.c - Latest tested: 3.17.1 (confirmed present)
Details
ext/oj/buf.h, line 61:
inline static void buf_append_string(Buf buf, const char *s, size_t slen) {
// ...
memcpy(buf->tail, s, slen); // slen derived from 32-bit int that wrapped negative
In parse.c, escape sequence handling computes the remaining string length as an int:
// parse.c:402 (read_escaped_str)
int slen = (int)(s - str); // ← wraps to negative when string > 2 GB
buf_append_string(buf, str, (size_t)slen); // ← (size_t)(-2147483648) = 0x80000000...
ASAN report:
==399019==ERROR: AddressSanitizer: negative-size-param: (size=-2147483648)
#0 __asan_memcpy
#1 buf_append_string /ext/oj/buf.h:61
#2 read_escaped_str /ext/oj/parse.c:402
#3 read_str /ext/oj/parse.c:542
#4 oj_parse2 /ext/oj/parse.c:882
#5 oj_pi_parse /ext/oj/parse.c:1256
#6 oj_object_parse /ext/oj/object.c:701
#7 load /ext/oj/oj.c:1259
0x7f5a26ff0801 is located 1 bytes inside of 2147483657-byte region [0x7f5a26ff0800, 0x7f5aa6ff0809)
Reproduce
require 'oj'
n = 1 << 31 # 2 GB
json = '"' + ('A' * n) + 'A"' # >2GB JSON string with a trailing escape
Oj.load(json)
Impact
An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value. Typical impact: incorrect size calculations leading to heap overflows or logic errors.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-54903? CVE-2026-54903 is a high-severity integer overflow or wraparound vulnerability in oj (rubygems), affecting versions < 3.17.2. It is fixed in 3.17.3. An arithmetic operation produces a value that exceeds the integer type's maximum, causing it to wrap to an unexpected small value.
- Which versions of oj are affected by CVE-2026-54903? oj (rubygems) versions < 3.17.2 is affected.
- Is there a fix for CVE-2026-54903? Yes. CVE-2026-54903 is fixed in 3.17.3. Upgrade to this version or later.
- Is CVE-2026-54903 exploitable, and should I be worried? Whether CVE-2026-54903 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-54903 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-54903? Upgrade
ojto 3.17.3 or later.