Summary
Oj: Use-After-Free in Oj::Doc Iterators via Reentrant Close
Oj::Doc iterators (each_value, each_child, each_leaf) are vulnerable to a heap use-after-free. When a Ruby block yielded during iteration calls doc.close or d.close, the document's heap memory is freed while the C iterator is still running. When control returns from the block, the iterator reads from the freed region, producing a use-after-free accessible from pure Ruby.
Version
- Software: oj gem
- Affected: all versions with
ext/oj/fast.c - Latest tested: 3.17.1 (confirmed present)
Details
The iterators in ext/oj/fast.c follow the pattern:
// fast.c:1505 (doc_each_child)
static VALUE doc_each_child(VALUE self, ...) {
...
while (cur != NULL) {
rb_yield(...); // ← Ruby block executes here
cur = cur->next; // ← cur is now freed if block called close()
}
}
rb_yield can invoke arbitrary Ruby code, including calling close() on the Doc or any child node, which calls ruby_sized_xfree on the backing buffer. On return, the C code reads cur->next from the freed region. All three iterators are affected.
ASAN report (each_child variant):
==253632==ERROR: AddressSanitizer: heap-use-after-free on address 0x5210000bd080
READ of size 8 at 0x5210000bd080 thread T0
#0 doc_each_child /ext/oj/fast.c:1505
0x5210000bd080 is located 896 bytes inside of 4064-byte region [0x5210000bcd00, 0x5210000bdce0)
freed by thread T0 here:
#0 free
#1 ruby_sized_xfree (libruby-3.3.so.3.3)
All three iterators trigger the same freed region (fd shadow bytes):
0x5210000bd080:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
Reproduce
require 'oj'
# each_child
Oj::Doc.open('[1,2]') { |doc| doc.each_child { |d| d.close } }
# each_value
Oj::Doc.open('[1,2]') { |doc| doc.each_value { |v| doc.close } }
# each_leaf
Oj::Doc.open('[1,[2]]') { |doc| doc.each_leaf { |d| d.close } }
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
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.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-54897? CVE-2026-54897 is a high-severity use after free vulnerability in oj (rubygems), affecting versions < 3.17.2. It is fixed in 3.17.3. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- Which versions of oj are affected by CVE-2026-54897? oj (rubygems) versions < 3.17.2 is affected.
- Is there a fix for CVE-2026-54897? Yes. CVE-2026-54897 is fixed in 3.17.3. Upgrade to this version or later.
- Is CVE-2026-54897 exploitable, and should I be worried? Whether CVE-2026-54897 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-2026-54897 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-2026-54897? Upgrade
ojto 3.17.3 or later.