[HIGH] Arbitrary local file content disclosure via [include] directive in untrusted .gitmodules (SubmoduleConfigParser never disables merge_includes)

• CWE: CWE-200 (Exposure of Sensitive Information) / CWE-73 (External Control of File Name or Path)
• Affected component: git/objects/submodule/base.py, Submodule._config_parser() (~line 273) constructing SubmoduleConfigParser(fp_module, read_only=read_only); git/config.py, GitConfigParser.__init__ (merge_includes default), GitConfigParser.read()/_included_paths() (include-path resolution, ~lines 630-685), GitConfigParser._read() (~line 493-498, MissingSectionHeaderError)
• Affected version: GitPython at HEAD (9729ed3b948f2bde09f1f188c5311e172212b67e, 2026-08-05, VERSION 3.1.58)

Reachability

GitConfigParser.__init__ defaults merge_includes=True: any config file it parses has its [include] (and, when a repo= is supplied, [includeIf ...]) directives followed and merged in. The maintainers already recognized this as dangerous for one specific case and fixed it in commit 41ecc6a4 ("Disable merge_includes in config writers"), which passes merge_includes=False when Repo.config_writer() builds its parser (git/repo/base.py).

That fix never touched Submodule._config_parser(). This method builds the parser used for every read of a repo's submodule configuration — repo.submodules, Submodule.iter_items(), Submodule.config() — via `SubmoduleConfigParser(fp_modu…