GHSA-83g3-92jg-28cx CVE-2026-26960

Arbitrary File Read/Write via Hardlink Target Escape Through Symlink Chain in node-tar Extraction

High npm

Severity: 7.1 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.33%; Chance of exploitation in the next 30 days. Higher than 26.00% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Fix: 7.5.8; Upgrade tar to this version or later

Description

Summary

tar.extract() in Node tar allows an attacker-controlled archive to create a hardlink inside the extraction directory that points to a file outside the extraction root, using default options.

This enables arbitrary file read and write as the extracting user (no root, no chmod, no preservePaths).

Severity is high because the primitive bypasses path protections and turns archive extraction into a direct filesystem access primitive.

Details

The bypass chain uses two symlinks plus one hardlink:

a/b/c/up -> ../..
a/b/escape -> c/up/../..
exfil (hardlink) -> a/b/escape/<target-relative-to-parent-of-extract>

Why this works:

Linkpath checks are string-based and do not resolve symlinks on disk for hardlink target safety.
- See STRIPABSOLUTEPATH logic in:
  - ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:255
  - ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:268
  - ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:281
Hardlink extraction resolves target as path.resolve(cwd, entry.linkpath) and then calls fs.link(target, destination).
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:566
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:567
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:703
Parent directory safety checks (mkdir + symlink detection) are applied to the destination path of the extracted entry, not to the resolved hardlink target path.
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:617
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/unpack.js:619
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/mkdir.js:27
- ../tar-audit-setuid - CVE/node_modules/tar/dist/commonjs/mkdir.js:101

As a result, exfil is created inside extraction root but linked to an external file. The PoC confirms shared inode and successful read+write via exfil.

PoC

hardlink.js Environment used for validation:

Node: v25.4.0
tar: 7.5.7
OS: macOS Darwin 25.2.0
Extract options: defaults (tar.extract({ file, cwd }))

Steps:

Prepare/locate a tar module. If require('tar') is not available locally, set TAR_MODULE to an absolute path to a tar package directory.
Run:

TAR_MODULE="$(cd '../tar-audit-setuid - CVE/node_modules/tar' && pwd)" node hardlink.js

Expected vulnerable output (key lines):

same_inode=true
read_ok=true
write_ok=true
result=VULNERABLE

Interpretation:

same_inode=true: extracted exfil and external secret are the same file object.
read_ok=true: reading exfil leaks external content.
write_ok=true: writing exfil modifies external file.

Impact

Vulnerability type:

Arbitrary file read/write via archive extraction path confusion and link resolution.

Who is impacted:

Any application/service that extracts attacker-controlled tar archives with Node tar defaults.
Impact scope is the privileges of the extracting process user.

Potential outcomes:

Read sensitive files reachable by the process user.
Overwrite writable files outside extraction root.
Escalate impact depending on deployment context (keys, configs, scripts, app data).

Affected versions

npm

Package	Vulnerable	Fixed in
tar	`< 7.5.8`	`7.5.8`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

tar npm → `7.5.8`

npm

npm install tar@7.5.8

yarn

yarn add tar@7.5.8

pnpm

pnpm add tar@7.5.8

Severity breakdown

CVSS 3.1 7.1

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Attack vector: Local
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Weakness

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

How to prevent it

Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would b
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked. Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (CWE-23, CWE-59). This includes: realpath() in C getCanonicalPath() in Java GetFullPath() in ASP.NET realpath() or abs_path() in Perl realpath() in PHP
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt". Features such as the ESAPI AccessReferenceMap [REF-185] provide this capability.
Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
Architecture and Design, Operation: Store library, include, and utility files outside of the web document root, if possible. Otherwise, store them in a separate directory and use the web server's access control capabilities to prevent attackers from directly requesting them. One common practice is to define a fixed constant in each calling program, then check for the existence of the constant in the library/include file; if the constant does not exist, then the file was directly requested, and it can exit immediately. This significantly reduces the chance of an attacker being able to bypass any protection mechanisms that are in the base program but not in the include files. It will also reduce the attack surface.
Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. In the context of path traversal, error messages which disclose path information can help attackers craft the appropriate attack strings to move through the file system hierarchy.
Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-26960

Packages

github.com/isaacs/node-tar

Timeline

Feb 18, 2026 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-r292-9mhp-454m node-tar: Uncontrolled recursion in mapHas/filesFilter allows uncatchable stack-overflow DoS via crafted long-path tar with member selection	High	Also affects tar
GHSA-gvwx-54wh-qm9j node-tar: Uncaught Exception DoS via NUL byte in PAX path/linkpath records	Medium	Also affects tar
GHSA-8x88-c5mf-7j5w node-tar: Negative tar entry size causes infinite loop in archive replace	High	Also affects tar
GHSA-23hp-3jrh-7fpw node-tar: Decompression/parse DoS via unlimited input	High	Also affects tar
GHSA-w8wr-v893-vjvp node-tar: Process crash via PAX numeric path type confusion	High	Also affects tar
GHSA-vmf3-w455-68vh node-tar applies PAX size override to intermediary GNU long-name/long-link headers, causing tar parser interpretation differential (file smuggling)	Medium	Also affects tar
GHSA-9ppj-qmqm-q256 node-tar Symlink Path Traversal via Drive-Relative Linkpath	Medium	Also affects tar
GHSA-qffp-2rhf-9h96 tar has Hardlink Path Traversal via Drive-Relative Linkpath	Medium	Also affects tar

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