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Medium, CVSS 5.3amended

isomorphic-git: Path traversal via a ".." tree-entry name writes files outside the working directory on clone/checkout

CVE-2026-63478GHSA-cw2g-2vwq-88w6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (isomorphic-git 1.38.6), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
EPSS
  • CVE-2026-63478: 0.29% estimated exploitation activity in the next 30 days; percentile 22.38 (FIRST EPSS, 2026-11-10). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary isomorphic-git's tree parser (`src/models/GitTree.js`) validates each entry name only against the path separators `/` and `\`. It does not reject the standalone reserved name `..`, so a malicious repository can, on a single `clone`/`checkout`, write files outside the working directory (unbounded depth). Works on any host-backed `fs` provider.

Details The guard is: ```js // src/models/GitTree.js if (path.includes('\\') || path.includes('/')) { throw new UnsafeFilepathError(path) } ``` The standalone string `..` passes. isomorphic-git assembles the full path incrementally across tree levels, so nesting `..` trees yields `../escaped.txt`, `../../escaped.txt`, … with unbounded depth (each level is a separate tree object that passes the per-entry guard). On checkout `mkdir(workdir/..)` hits `EEXIST` (ignored) and the file is written above the working directory. Depth is chosen to reach the home dir, `/etc`, `/tmp`, etc.; overwriting a shell rc / config / startup file…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-cw2g-2vwq-88w6

  2. Revision 1 · created ·

    Published from ghsa record GHSA-cw2g-2vwq-88w6

Agent brief

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# Patch Next advisory brief: CVE-2026-63478

Advisory: isomorphic-git: Path traversal via a ".." tree-entry name writes files outside the working directory on clone/checkout
IDs: CVE-2026-63478, GHSA-cw2g-2vwq-88w6
Record: https://patchnext.com/advisories/cve-2026-63478 (revision 2, source checked 10 Nov 2026, 06:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: isomorphic-git 1.38.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm isomorphic-git: affected < 1.38.6; fixed in 1.38.6

## Suggested inspection (read-only)
- `npm ls isomorphic-git --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on isomorphic-git.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-cw2g-2vwq-88w6 (GitHub-reviewed advisory GHSA-cw2g-2vwq-88w6 lists affected ranges: npm isomorphic-git >=0 <=1.38.5)
- Verified: https://osv.dev/vulnerability/GHSA-cw2g-2vwq-88w6 (OSV record GHSA-cw2g-2vwq-88w6 lists affected ranges: npm isomorphic-git >=0 <1.38.6 (fixed))

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