CVE-2026-54500 Oj: intern.c form_attr has an uninitialized stack read
An attacker can leak process stack memory by providing long JSON keys to the Oj Ruby gem, potentially exposing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54500?
CVE-2026-54500 is a medium-severity vulnerability in ohler55 oj, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.3, Oj.load in :object mode reads uninitialized stack memory (and, for long keys, reads out of bounds) when parsing a JSON object whose key is 254 bytes or longer. The interned bytes can surface to the caller, disclosing process stack memory. In ext/oj/intern.c, form_attr() handles the long-key path by allocating a heap buffer, `b`, populating it with the attribute name, and then freeing it — but it passed the uninitialized stack buffer buf (not b) to rb_intern3(). rb_intern3 therefore reads len + 1 bytes of uninitialized stack memory. When the key length is >= 256, it also reads out of bounds past the 256-byte buf. The resulting bytes are interned and can reach the caller via the produced Symbol or via the EncodingError message raised on invalid UTF-8, leaking process stack contents. This issue has been fixed in version 3.17.3.
Which versions are affected by CVE-2026-54500?
2 open source packages ship an affected version, including oj.
| Package | Affected | Fixed in |
|---|---|---|
oj RubyGems | All versions | 3.17.3 |
oj RubyGems | All versions | 3.17.3 |
How do I fix CVE-2026-54500?
Upgrade oj to 3.17.3 or later.
Is CVE-2026-54500 being exploited?
There is no known exploitation of CVE-2026-54500 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-54500, GHSA-fm7p-mprw-wjm9, MINI-j4wq-cp5r-ccw7, MINI-mf4v-6r96-q95f, MINI-pj8f-8jhg-c29w, MINI-pm74-89rf-8jxr and 2 more.