isomorphic-git: Arbitrary file write outside the working tree via a directory symlink during checkout (potential RCE)
Affects isomorphic-git versions 1.38.5 and earlier, which can write files outside the working tree during checkout via a directory symlink. Fixed in 1.38.6.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- Proof of concept public, per CISA
- Fix
- Fixed in 1.38.6
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Affects isomorphic-git versions prior to 1.38.6 (affected versions <= 1.38.5).
- Exploitation15/40CISA rates a proof of concept as public
- Exposure12/25Specific setups only, reachable over the network without a login
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity9.8/10CVSS 8.8, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
CVE-2026-63395 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects isomorphic-git; fixed in 1.38.6.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 37/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Fix
- Fixed in 1.38.6
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: poc
- Automatable: no
- Technical impact: total
Summary
isomorphic-git, a pure JavaScript Git implementation used in Node.js and browser applications, is affected when its checkout process writes files through symlinked directories. A malicious repository can use this to write files outside the working tree on Linux or macOS, potentially allowing arbitrary host file overwrites and code execution.
Read the original description
isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git's git.checkout writes new child paths through symlinked leading directory components without checking them. A malicious repository can first place a directory symlink and later replace the tree state with a child file beneath that path; the usual trigger is a clone followed by a later pull, while a single clone can trigger the issue when a symlink already exists or the consuming application accesses the tree. With Node fs on Linux or macOS, the operating system can resolve the write outside the working tree, permitting arbitrary host file writes and possible code execution. Node fs on Windows usually blocks the symlink plant without additional privilege, and browser or in-memory providers limit impact to their virtual filesystem and are affected only when they implement symlink creation and following. This issue is fixed in version 1.38.6.
What to do
Check whether your setup matches what the bug needs.
Affects isomorphic-git versions prior to 1.38.6 (affected versions <= 1.38.5).Upgrade to a fixed version: 1.38.6.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: no · Technical impact: total
- Record last updated
Affected versions
- isomorphic-git isomorphic-git
fixed in 1.38.6
Evidence 4
- Advisory
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-63395
Is CVE-2026-63395 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
During checkout, a directory symlink can cause isomorphic-git to write files outside the working tree. The advisory title notes this could lead to remote code execution.Source: github.com
Which versions are affected by CVE-2026-63395?
isomorphic-git: before 1.38.6.Source: cve.now feed data
Am I affected, and how do I check?
Versions 1.38.5 and earlier are affected. To check a project's version, look at the isomorphic-git entry in its package.json or run npm ls isomorphic-git.Source: github.com
How do I fix CVE-2026-63395?
Upgrade isomorphic-git to 1.38.6 or later.Source: github.com