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Fencer Intel
high 7.4

CVE-2026-76844 json

zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write

published 2mo ago modified 30d ago also EUVD-2026-64850 , GHSA-g84c-rxfj-3j2c

cvss
7.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

Summary

zlib 1.2.11 through 1.3.2 contains a heap buffer overflow: after an underlying write() fails, gz_write() returns without resetting strm.next_in, leaving it pointed at the caller's buffer. A later gz* write call then derives a position from the stale pointer and writes past a heap allocation; any write() failure reaches it, including EPIPE on a blocking descriptor, and in versions before 1.3.1.2 the failed write must be followed by a gzclearerr() call.

Patch / fix

  • npm webpack-dev-middleware 7.4.6, 8.3.0
  • zlib Debian 13 1:1.3.dfsg+really1.3.1-1+deb13u1
  • zlib Debian 14 1:1.3.dfsg+really1.3.2-4

debian advisories DEBIAN-CVE-2026-76844

  • zlib Azure Linux 3.0 1.3.2-2

azure linux advisories AZL-105345

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Is CVE-2026-76844 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2026-76844 updated cvss 8.1

zlib: zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write

  • Red Hat Data Grid 8.6.3
    fixed: vendor fix RHSA-2026:69296
  • Red Hat Discovery 2 discovery/discovery-ui-rhel9 1788206196
    fixed: vendor fix RHSA-2026:61783
  • Red Hat Migration Toolkit 1.8 rhmtc/openshift-migration-ui-rhel8 1789546373
    fixed: vendor fix RHSA-2026:68681
  • Red Hat OpenShift AI 3.4 rhoai/odh-feature-server-rhel9 1792685074
    fixed: vendor fix RHSA-2026:92510
  • Red Hat Discovery 2 discovery/discovery-server-rhel9 1788205779 Red Hat Migration Toolkit 1.8 rhmtc/openshift-migration-openvpn-rhel8 1789447887, rhmtc/openshift-migration-registry-rhel8 1789447846, rhmtc/openshift-migration-rhel8-operator 1789546352, rhmtc/openshift-migration-operator-bundle 1789546820, rhmtc/openshift-migration-controller-rhel8 1789377223, rhmtc/openshift-migration-log-reader-rhel8 1789375331, +4 more Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1792722177, rhoai/rhai-cli-rhel9 1792722177, rhoai/odh-automl-rhel9 1792697253, rhoai/odh-mlflow-rhel9 1793002327, rhoai/odh-autorag-rhel9 1793265800, rhoai/odh-trainer-rhel9 1792817113, +99 more
    not affected: vulnerable code not present

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
2mo ago

Exploit prediction

0.59% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • gist.github.com https://gist.github.com/thesmartshadow/e0b9481792afb7c31e86fee1ff084490 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
GitHub 3.1 7.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
CNA 4.0 8.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm webpack-dev-middleware
>=8.0.0, <8.3.0
<7.4.6
8.3.0
7.4.6

Affected products

  • zlib zlib

Classification

Weakness
  • CWE-787 Out-of-bounds Write
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory

References

Sources

Fencer Intel 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.

The maintainers of webpack/webpack-dev-middleware published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.