VulnerabilityPublished 10 Jul 2026

CVE-2026-39243: decompress · Link Following

Affects decompressSource CVE Database V5

Not known to be exploited · CVSS 5.5 Medium : upgrade to 4.2.2 when convenient.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

5.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 22% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.2.2

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

Attack Vector: Local
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade decompress to 4.2.2.

Affected software

Product	Affected	Fixed in
npmdecompress`pkg:npm/decompress`Other threats	Affected <4.2.2	Fixed in 4.2.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available for decompress that fixes this vulnerability in version 4.2.2. Users should upgrade to version 4.2.2 or later to remediate this issue. Until patched, avoid extracting untrusted archives with decompress or implement additional validation on archive contents to prevent hardlink exploitation.

Description

A vulnerability in decompress versions before 4.2.2 allows an attacker to create arbitrary hardlinks during archive extraction. This occurs because the x.linkname field from the archive is used without validation when processing hardlink entries, enabling an attacker to link to any file on the same filesystem. This can lead to unauthorized reading and overwriting of files, causing file disclosure and corruption. The vulnerability is limited to files on the same filesystem and does not affect directories. A patch is available to address this issue.

Impact

Successful exploitation allows an attacker with the ability to supply archive files to cause arbitrary file read disclosure and file corruption on the target system by creating hardlinks to existing files. This can compromise confidentiality and integrity of files on the same filesystem as the extraction directory. The attack requires local access or the ability to influence archive extraction and does not affect availability.

Summary

The decompress library before version 4.2.2 contains a vulnerability (CVE-2026-39243) where the x.linkname field in hardlink entries is passed directly to fs.link() without validation. This allows an attacker to craft an archive with a hardlink entry pointing to an absolute path of any file on the same filesystem. During extraction, this creates a hardlink inside the extraction directory that shares the inode with the target file, enabling both reading and overwriting of the original file's content. The vulnerability is classified under CWE-59 (Improper Link Resolution Before File Access).

CWE-59Improper Link Resolution Before File Access ('Link Following') (opens in a new tab)
Base weaknessLikelihood of exploit: MediumOWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
Architecture and Design · Separation of Privilege
Follow the principle of least privilege when assigning access rights to entities in a software system.
OWASP Cheat Sheets
Authorization (opens in a new tab)
Attack patterns
Symlink Attack (opens in a new tab)
Using Malicious Files (opens in a new tab)
Leverage Executable Code in Non-Executable Files (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Aug 2026, 18:10 UTC

WeaknessesCWE-59

Technical details

References

Community reviews

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