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Fencer Vulns
medium 5.5

CVE-2026-39243 json

decompress allows arbitrary hardlink creation during archive extraction

published 2026-07-09 4 mo ago modified 2026-08-13 2 mo ago also GHSA-jwp9-9v96-94mx , EUVD-2026-42768

cvss
5.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 23%
public exploits
0
none known

Summary

decompress before 4.2.2 allows arbitrary hardlink creation during archive extraction, enabling file read disclosure and file corruption. When processing hardlink entries (type === 'link'), the x.linkname field from the archive is passed directly to fs.link() without validation (index.js line 113). An attacker can craft an archive with a hardlink entry whose linkname is an absolute path to any file on the same filesystem. This creates a hardlink inside the extraction directory that shares the same inode as the target file, enabling both reading and overwriting the original file's content. Hardlinks are limited to files on the same filesystem and cannot target directories.

Patch / fix

  • dotnet8.0 hummingbird 1 8.0.128-1.1.hum1
  • dotnet-sdk-8.0 hummingbird 1 8.0.128-1.1.hum1
  • dotnet-hostfxr-8.0 hummingbird 1 8.0.28-1.1.hum1
  • dotnet-runtime-8.0 hummingbird 1 8.0.28-1.1.hum1
  • dotnet-sdk-dbg-8.0 hummingbird 1 8.0.128-1.1.hum1
  • dotnet-templates-8.0 hummingbird 1 8.0.128-1.1.hum1
  • aspnetcore-runtime-8.0 hummingbird 1 8.0.28-1.1.hum1
  • dotnet-runtime-dbg-8.0 hummingbird 1 8.0.28-1.1.hum1

red hat advisories RHSA-2026:37577

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-39243 updated cvss 6.1

decompress: Decompress: File disclosure and corruption via arbitrary hardlink creation

  • Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/volsync-rhel9, rhacm2/volsync-operator-bundle Red Hat Build of Keycloak decompress 4.2.1
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images dotnet8.0 8.0.128-1.1.hum1, aspnetcore-runtime-8.0 8.0.28-1.1.hum1
    fixed: vendor fix RHSA-2026:37577

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/kevva/decompress/issues/113 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
CNA 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
GitHub 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
npm decompress
<=4.2.1
 no fix listed

Classification

Weakness
  • CWE-59 Improper Link Resolution Before File Access

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.