zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write
Priority HIGH 69CWE-787Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · High · High
- Fix status
- Partial Red Hat: 4 fixed, 12 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00592 48th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by the CNA
Fix Partial webpack-dev-middleware (npm): 8.3.0, 7.4.6Red Hat: 4 advisoriesRed Hat: 4 fixed, 12 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| zlib | zlib | 1.2.11 – 1.3.2 | — | No fix listed | CNA |
| — | webpack-dev-middleware (npm) | 8.0.0 to before 8.3.0 | 8.3.0 | Patch available | GHSA-g84c-rxfj-3j2c |
| — | webpack-dev-middleware (npm) | before 7.4.6 | 7.4.6 | Patch available | GHSA-g84c-rxfj-3j2c |
- zlib Vendorzlib Affected 1.2.11 – 1.3.2 Fixed in — No fix listed CNA
- webpack-dev-middleware (npm) Vendor— Affected 8.0.0 to before 8.3.0 Fixed in 8.3.0 Patch available GHSA-g84c-rxfj-3j2c
- webpack-dev-middleware (npm) Vendor— Affected before 7.4.6 Fixed in 7.4.6 Patch available GHSA-g84c-rxfj-3j2c
Remediation
- Fix · GHSA-g84c-rxfj-3j2c webpack-dev-middleware (npm) Fixed in 8.3.0 Advisory →
- Fix · GHSA-g84c-rxfj-3j2c webpack-dev-middleware (npm) Fixed in 7.4.6 Advisory →
Red Hat 4 advisories
- RHSA-2026:92510 Released 2026-10-29 · Red Hat rating CriticalRHOAI 3.4.6 - Red Hat OpenShift AI
- Red Hat OpenShift AI 3.4 registry.redhat.io/rhoai/odh-built-in-detector-rhel9, registry.redhat.io/rhoai/odh-cli-rhel9, registry.redhat.io/rhoai/odh-dashboard-rhel9 +47
- RHSA-2026:69296 Released 2026-09-21 · Red Hat rating ImportantRed Hat Data Grid 8.6.3 security update
- Red Hat Data Grid 8.6.3
- RHSA-2026:68681 Released 2026-09-17 · Red Hat rating ImportantMigration Toolkit for Containers (MTC) 1.8.17 update
- Red Hat Migration Toolkit 1.8 registry.redhat.io/rhmtc/openshift-migration-registry-rhel8, registry.redhat.io/rhmtc/openshift-migration-ui-rhel8
Show 1 more Red Hat advisories
- RHSA-2026:61783 Released 2026-08-31 · Red Hat rating ImportantA Subscription Management tool for finding and reporting Red Hat product usage
- Red Hat Discovery 2 registry.redhat.io/discovery/discovery-server-rhel9, registry.redhat.io/discovery/discovery-ui-rhel9
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Node HealthCheck Operator | Affected | No fix yet |
| OpenShift Pipelines | Affected | No fix yet |
| Red Hat Ansible Automation Platform 2 | Affected | No fix planned: Will not fix |
| Red Hat Build of Podman Desktop | Affected | No fix yet |
| Red Hat Ceph Storage 4 | Affected | No fix yet: Fix deferred |
| Red Hat Developer Hub 1 | Affected | No fix yet |
| Red Hat Enterprise Linux AI (RHEL AI) 3 | Affected | No fix yet |
| Red Hat Fuse 7 | Affected | No fix planned: Will not fix |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet |
| Red Hat OpenShift GitOps | Affected | No fix planned: Will not fix |
| Red Hat build of Apache Camel - HawtIO 4 | Affected | No fix planned: Will not fix |
| Secrets Management Console for Red Hat OpenShift | Affected | No fix planned: Will not fix |
| Red Hat Data Grid 8.6.3 | Fixed | RHSA-2026:69296 |
| Red Hat Discovery 2 | Fixed | RHSA-2026:61783 |
| Red Hat Migration Toolkit 1.8 | Fixed | RHSA-2026:68681 |
| Red Hat OpenShift AI 3.4 | Fixed | RHSA-2026:92510 |
Not affected: 21 products
- Gatekeeper 3
- OpenShift Lightspeed
- OpenShift Service Mesh 3
- Red Hat 3scale API Management Platform 2
- Red Hat AMQ Broker 7
- Red Hat Ansible Automation Platform 2
- Red Hat Connectivity Link 1
- Red Hat Developer Hub 1
- Red Hat Discovery 2
- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Red Hat Hardened Images
- Red Hat Migration Toolkit 1.8
- Red Hat OpenShift AI 3.4
- Red Hat OpenShift Container Platform 4
- Red Hat OpenShift GitOps
- Red Hat Quay 3
- Red Hat Satellite 6
- Red Hat build of Apache Camel for Spring Boot 4
- Self-service automation portal 2
Timeline
- 2026-10-02 Threatist record created from CVE-2026-76844
- 2026-10-03 Alias added: GHSA-g84c-rxfj-3j2c
- 2026-10-06 Affected versions changed · Red Hat
- 2026-10-18 Affected versions changed · Red Hat
- 2026-10-27 Affected versions changed · Red Hat
- 2026-10-30 Fix available: RHSA-2026:92510 · Red Hat
- 2026-10-30 Fix available: Red Hat OpenShift AI 3.4 · Red Hat
References
Patch 1
Advisory 2
Other 10
- https://github.com/madler/zlib/blob/v1.3.2/gzwrite.c#L393
- https://github.com/madler/zlib
- https://github.com/webpack/webpack-dev-middleware/security/advisories/GHSA-g84c-rxfj-3j2c
- https://github.com/webpack/webpack-dev-middleware/pull/2404
- https://github.com/webpack/webpack-dev-middleware/commit/13344e78b26d88fe9b7c8381a3860e248a52359b
- https://github.com/webpack/webpack-dev-middleware/commit/cefccbac330c29052fc6dffe85fd292ea2ac782b
- https://github.com/webpack/webpack-dev-middleware
- https://github.com/webpack/webpack-dev-middleware/blob/v8.1.1/src/middleware.js
- https://github.com/webpack/webpack-dev-middleware/releases/tag/v7.4.6
- https://github.com/webpack/webpack-dev-middleware/releases/tag/v8.3.0
More zlib vulnerabilities
- TI-2022-17498 zlib through 1.2.12 has a heap-based buffer over-read or buffer overflow in inflate in… CVSS 3.1CRITICAL 9.8
- TI-2018-15259 zlib before 1.2.12 allows memory corruption when deflating (i.e., when compressing) if… CVSS 3.1HIGH 7.5
- TI-2026-58450 zlib 1.3.1.2 through 1.3.2 Heap Buffer Overflow via gz_vacate CVSS 4.0HIGH 8.3
- TI-2026-17794 zlib <= 1.3.1.2 untgz Global Buffer Overflow in TGZfname() CVSS 4.0MEDIUM 4.6
- TI-2016-07970 inffast.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified… CVSS 3.1CRITICAL 9.8
- TI-2026-21613 zlib before 1.3.2 allows CPU consumption via crc32_combine64 and crc32_combine_gen64… CVSS 3.1MEDIUM 5.5
Sources
- CVE-2026-76844 · CVE Program
- CVE-2026-76844 · NVD
- FIRST EPSS
- GHSA-g84c-rxfj-3j2c · GitHub Advisory Database · CC BY 4.0
- CVE-2026-76844 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences