# CVE-2026-76844: zlib 1.2.11 through 1.3.2 Heap Buffer Overflow via Stale gzwrite Pointer After Failed Write

> Heap buffer overflow in zlib allows attackers to execute arbitrary code or cause denial of service via stale pointers after write failures.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Aug 2026
- **Updated:** 1 Oct 2026
- **Also known as:** AZL-105345, CLSA-2026-1787602147, CLSA-2026-1790604916, CLSA-2026-1790755864, CLSA-2026-1790756051, CLSA-2026-1790876768, CLSA-2026-1790884229, CLSA-2026-1791506807, CLSA-2026-1791666312, CLSA-2026-1791666413, CLSA-2026-1791666532, CLSA-2026-1791666638, CLSA-2026-1791677094, CLSA-2026-1791830789, CLSA-2026-1791832293, CLSA-2026-1791907762, CLSA-2026-1791907870, CLSA-2026-1791915688, CLSA-2026-1791916248, CLSA-2026-1791969403, CLSA-2026-1791970344, CLSA-2026-1791973683, CLSA-2026-1793108549, CLSA-2026-1793112587, ECHO-355f-9f1c-25e5, GHSA-g84c-rxfj-3j2c, MINI-4f5p-q8w6-j6xj, MINI-9xv9-9gj3-hfmr, MINI-f3w6-59c6-v6x5, MINI-gr24-6xrg-7m8w, MINI-q2x7-4r8x-676x, MINI-wpc4-jqx9-vx25, ROOT-APP-NPM-CVE-2026-76844

## What is CVE-2026-76844?

CVE-2026-76844 is a high-severity memory corruption vulnerability in zlib, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-76844?

4 open source packages ship an affected version, including webpack-dev-middleware.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `webpack-dev-middleware` | npm | All versions | 7.4.6 |
| `webpack-dev-middleware` | npm | All versions | 7.4.6 |
| `webpack-dev-middleware` | npm | From 8.0.0 | 8.3.0 |
| `webpack-dev-middleware` | npm | From 8.0.0 | 8.3.0 |

## How do I fix CVE-2026-76844?

Upgrade webpack-dev-middleware to a fixed version for your release line: 7.4.6 or 8.3.0.

## Is CVE-2026-76844 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-76844 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-76844 and fix it if it is affected.

What it is: CVE-2026-76844 is a high-severity memory corruption vulnerability in zlib, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-76844 exists.

Affected packages and fixed versions:
- webpack-dev-middleware (npm): affected all versions; fixed in 7.4.6
- webpack-dev-middleware (npm): affected all versions; fixed in 7.4.6
- webpack-dev-middleware (npm): affected from 8.0.0; fixed in 8.3.0
- webpack-dev-middleware (npm): affected from 8.0.0; fixed in 8.3.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-76844/ (Markdown: https://insights.sbomify.com/CVE-2026-76844/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-76844
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-76844
- OSV: https://osv.dev/vulnerability/CVE-2026-76844

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-76844/
Summaries are generated and may contain mistakes; the official description above is the record.