GitLab CE

GitLab CE/EE RCE via the Jupyter-notebook diff renderer and two ~5-year-old Oj Ruby-parser memory-corruption bugs, public PoC, silent patch, no CVE

depthfirst disclosed (2026-07-24) a remote-code-execution chain against default self-managed GitLab CE/EE, reached through GitLab's in-tree ipynbdiff gem, which calls Oj::Parser.usual.parse (the native-C implementation of the Oj Ruby JSON parser) whenever a commit diff contains a .ipynb (Jupyter notebook) file (depthfirst, 2026-07-24). Two Oj memory-safety bugs that had survived in the parser for nearly five years (introduced 2021-08-08, first shipped in Oj 3.13.0, and reachable in GitLab from 15.2.0 once notebook validation switched to Oj in July 2022) are combined: an unchecked 16-bit key-length narrowing truncates an oversized object key and causes GitLab's notebook-diff output to print a live heap pointer (used to defeat ASLR and locate libc/libruby), and an unchecked nesting-stack overflow in Oj::Parser.usual.parse supplies a write primitive that redirects a parser callback to system(). The whole chain needs no elevated access, in depthfirst's words, "A normal authenticated user able to create or push to a project and view the resulting commit diff could commit an .ipynb file" (depthfirst, 2026-07-24), no admin rights, no CI/runner access, no victim interaction, by committing two crafted notebooks and requesting the commit diff (GET /<project>/-/commit/<sha>/diffs_stream).

The affected range is GitLab CE/EE 15.2.0–18.10.7, 18.11.0–18.11.4 and 19.0.0–19.0.1; GitLab shipped the fixed Oj (3.17.3) in its 10 June 2026 releases 18.10.8, 18.11.5 and 19.0.2 (The Hacker News, 2026-07-25). The operationally important detail is that GitLab did not record the fix in its security-fix table and no CVE was assigned to the GitLab chain, so any operator that tracks GitLab patching against the vendor's security-advisory feed missed it for the 44 days between the silent 10 June bump and the 2026-07-24 PoC publication; GitLab.com and Dedicated instances were already patched, but self-managed operators must act. A separate set of nine Oj advisories (covering the dumper, loader, SAJ callback and document APIs, each with its own CVE) came out of the same depthfirst review and are also fixed in Oj 3.17.3. No in-the-wild exploitation is reported; this is a disclosed researcher PoC.