{"id":"GHSA-x6jw-m9v5-85vh","summary":"simple-git unsafe-operation guard does not block trailer command configuration","details":"## Affected product\n\nThe default `blockUnsafeOperationsPlugin` in `simple-git` when an application permits untrusted values to reach `SimpleGitOptions.config` or Git inline configuration arguments such as `-c \u003ckey\u003e=\u003cvalue\u003e`.\n\n## Summary\n\n`trailer.\u003ctoken\u003e.cmd` is not recognized as unsafe by the default guard. Therefore, a configured inline value reaches Git without a `GitPluginError`.\n\nGit documents `trailer.\u003ctoken\u003e.cmd` as a shell command invoked by `git interpret-trailers`. An application that relies on the default plugin to reject unsafe configuration can therefore execute a command supplied through an untrusted trailer-command configuration value.\n\n## Technical details\n\n`simple-git/src/lib/git-factory.ts` installs `commandConfigPrefixingPlugin` before `blockUnsafeOperationsPlugin`. The prefixing plugin in `simple-git/src/lib/plugins/command-config-prefixing-plugin.ts` turns every `SimpleGitOptions.config` entry into `-c \u003ckey\u003e=\u003cvalue\u003e` before the unsafe-operation plugin evaluates the final argv.\n\nIn `simple-git@3.36.0`, `blockUnsafeOperationsPlugin` delegates to `@simple-git/argv-parser`. `packages/argv-parser/src/vulnerabilities/detect-vulnerable-config-writes.ts` compares parsed configuration writes against `preventUnsafeConfig`. That list has no matcher for `trailer.\u003ctoken\u003e.cmd`, so the invocation is allowed.\n\nGit v2.39.5's `Documentation/git-interpret-trailers.txt` states that `trailer.\u003ctoken\u003e.cmd` specifies a shell command called to generate or modify a trailer.\n\n## Preconditions\n\nThe application must use an affected `simple-git` version with the default unsafe-operation plugin active and must pass attacker-controlled data into instance configuration or Git command arguments that configure `trailer.\u003ctoken\u003e.cmd`.\n\nThe invoked Git binary must support the documented trailer-command behavior, and the application must execute `git interpret-trailers` with the attacker-controlled configuration in scope. The command runs with the operating-system identity and permissions of the Node.js process.\n\n## Verification\n\nUse an isolated test environment and a harmless executable test helper that records only its invocation.\n\n**Control:** Configure `core.editor=\u003ctest-helper\u003e` through `SimpleGitOptions.config` and invoke a benign Git task. The default plugin should throw `GitPluginError` before spawning Git because `core.editor` is present in `preventUnsafeConfig`.\n\n**Bypass:** Configure `trailer.audit.cmd=\u003ctest-helper\u003e` through the same option and invoke Git with the equivalent argv shape:\n\n`git -c trailer.audit.cmd=\u003ctest-helper\u003e interpret-trailers --trailer audit:\u003cvalue\u003e \u003cinput-file\u003e`\n\nA vulnerable build does not raise `GitPluginError`; Git invokes the test helper while processing the trailer. Confirm the helper invocation, then remove test artifacts.\n\n## Impact\n\nAn attacker who controls the stated configuration input can cause Git to execute a shell command as the Node.js application process. The impact is bounded by that process's filesystem, network, and service permissions. Applications that do not expose untrusted configuration or command arguments to `simple-git` are outside this threat model.\n\n## Affected versions\n\nCommit `6b3c631eadea81f80ed10f6dec7d19a9db4d7084` introduced the default unsafe-operation plugin, and `simple-git@3.15.0` is the first release confirmed to contain it. Its implementation only rejected `protocol.allow` configuration, leaving trailer-command configuration unblocked.\n\nThe latest `simple-git` release, `3.36.0`, still lacks a trailer-command matcher. The current `main` branch also lacks one. No released remediation was identified.\n\n## Remediation\n\nDefault-deny configuration keys that can trigger executable behavior, or add a dedicated unsafe category that rejects `trailer.\u003ctoken\u003e.cmd` before spawning Git unless the application explicitly opts in.\n\nEvaluate `trailer.\u003ctoken\u003e.command` alongside `.cmd`, because Git documents it as related command behavior. Add parser and integration tests for leading `-c`, configured instance prefixes, and `git config` write forms, asserting that no Git child process is spawned without an explicit unsafe opt-in.\n\n## Evidence\n\n- `simple-git@3.15.0` was released on 2022-11-12 and contains the initial unsafe-operation plugin.\n- `simple-git@3.36.0` was released on 2026-04-12; its parser source does not match `trailer.\u003ctoken\u003e.cmd`.\n- `main` retains the missing matcher in `packages/argv-parser/src/vulnerabilities/detect-vulnerable-config-writes.ts`.\n- Git v2.39.5 documents the trailer command behavior in `Documentation/git-interpret-trailers.txt`.\n- PR #1167 expanded other configuration checks but did not add a trailer-command matcher and is not release-backed as a remediation.\n- This review verified repository, release, and source artifacts through GitHub; it did not independently execute the runtime reproduction.","aliases":["CVE-2026-102828"],"modified":"2026-10-06T00:00:11.872622278Z","published":"2026-10-05T23:48:14Z","database_specific":{"github_reviewed_at":"2026-10-05T23:48:14Z","nvd_published_at":"2026-09-29T19:17:25Z","cwe_ids":["CWE-184","CWE-78"],"severity":"CRITICAL","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/steveukx/git-js/security/advisories/GHSA-x6jw-m9v5-85vh"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-102828"},{"type":"WEB","url":"https://github.com/steveukx/git-js/pull/1198"},{"type":"WEB","url":"https://github.com/steveukx/git-js/commit/d762810c13b331ff1e5eb24c0b434646d2a8d1b3"},{"type":"PACKAGE","url":"https://github.com/steveukx/git-js"},{"type":"WEB","url":"https://github.com/steveukx/git-js/releases/tag/simple-git@4.0.1"}],"affected":[{"package":{"name":"simple-git","ecosystem":"npm","purl":"pkg:npm/simple-git"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.15.0"},{"fixed":"4.0.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-x6jw-m9v5-85vh/GHSA-x6jw-m9v5-85vh.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"}]}