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High, CVSS 8.8amended

isomorphic-git: Arbitrary file write outside of working tree via directory symlink during checkout (potential RCE)

CVE-2026-63395GHSA-9qw7-j9xw-fv9c

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
8.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-63395: 0.72% estimated exploitation activity in the next 30 days; percentile 54.10 (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 `git.checkout` writes working-tree files through a directory symlink without checking the leading path, so a malicious repository can write outside the intended working directory. The defect is in isomorphic-git's checkout logic itself and is therefore independent of the `fs` provider. The *impact* depends on the configured filesystem; worst case is arbitrary file write on the host, e.g. injecting an attacker key into `~/.ssh/authorized_keys` → remote login / code execution.

Details A single git tree can't hold a name as both a symlink and a directory, so the attack uses two states: ``` Commit N: config (mode 120000, symlink → ../.ssh) Commit N+1: config/ (mode 040000, tree) authorized_keys (mode 100644, attacker public key) ``` Checking out commit N writes `config` as a directory symlink. Checking out commit N+1 sees `config/authorized_keys` as a new path: isomorphic-git `mkdir`s the parent (`config`, already a symlink → `EEXIST`, ignored) then…

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

    Amended from osv record GHSA-9qw7-j9xw-fv9c

  2. Revision 1 · created ·

    Published from ghsa record GHSA-9qw7-j9xw-fv9c

Agent brief

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# Patch Next advisory brief: CVE-2026-63395

Advisory: isomorphic-git: Arbitrary file write outside of working tree via directory symlink during checkout (potential RCE)
IDs: CVE-2026-63395, GHSA-9qw7-j9xw-fv9c
Record: https://patchnext.com/advisories/cve-2026-63395 (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: High (CVSS 8.8)
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-9qw7-j9xw-fv9c (GitHub-reviewed advisory GHSA-9qw7-j9xw-fv9c lists affected ranges: npm isomorphic-git >=0 <=1.38.5)
- Verified: https://osv.dev/vulnerability/GHSA-9qw7-j9xw-fv9c (OSV record GHSA-9qw7-j9xw-fv9c lists affected ranges: npm isomorphic-git >=0 <1.38.6 (fixed))

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