How severe is CVE-2026-76844?

No CVSS score has been assigned to CVE-2026-76844 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-76844?

CVE-2026-76844 affects the following packages: webpack-dev-middleware (npm), webpack-dev-middleware (npm). Ecosystems affected: npm.

How do I fix CVE-2026-76844?

Update webpack-dev-middleware to 8.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-76844 is resolved across your whole dependency graph.

How do I detect CVE-2026-76844 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for webpack-dev-middleware, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-76844 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2026-76844 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-76844 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-76844?

CVE-2026-76844 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 47th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-76844?

CVE-2026-76844 is classified as Out-of-bounds Write (CWE-787). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-76844 published, and has it been updated?

CVE-2026-76844 was published on August 24, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-76844 — webpack-dev-middleware

Fix: madler/zlib@df84af2

CVE-2026-76844 is a Out-of-bounds Write vulnerability in webpack-dev-middleware. A fix is available for webpack-dev-middleware — see the affected versions and patch details below.

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

Also known asGHSA-g84c-rxfj-3j2c

Published

Aug 24, 2026

Updated

Oct 21, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 14, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-76844.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk+0.11%

Lower risk than most CVEs47th percentile — riskier than 47% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

3Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

webpack-dev-middlewarenpm

23.9Mdownloads / week

Description

[!IMPORTANT] CVE-2026-76844 was assigned and published for this issue by VulnCheck on 2026-08-24 without prior coordination with the webpack maintainers or the OpenJS Foundation, which holds the CVE Numbering Authority scope for webpack projects. Neither the maintainers nor the OpenJS CNA were notified before publication, and no fix was available at that time. This advisory is the coordinated record produced by the webpack maintainers and the OpenJS Foundation CNA.

Impact

webpack-dev-middleware resolves a request to a local file in getFilenameFromUrl. When the configured publicPath has no trailing slash (for example /assets), a request that shares that prefix without being under it (for example /assets../secret) still passes the containment check, and the .. guard does not catch it because it runs on the path before the publicPath prefix is stripped. The stripped remainder then escapes the configured output directory once joined, so an unauthenticated request can read files outside the output root. Applications serving webpack-dev-middleware (directly or via webpack-dev-server) with a publicPath that does not end in a slash are affected. A development server reachable on the network can be attacked with a single request and no victim interaction.

Patches

Patched in webpack-dev-middleware 8.3.0. There is no backport to the 5.x, 6.x, or 7.x lines; users on those lines should upgrade to 8.3.0 or later.

Workarounds

Configure publicPath with a trailing slash (for example /assets/ instead of /assets), or upgrade to a patched version.

References

CVE-2024-29180 (GHSA-wr3j-pwj9-hqq6), the earlier path traversal in the same component that this issue bypasses.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`webpack-dev-middleware`	≥ 8.0.0&&< 8.3.0	8.3.0`npm install webpack-dev-middleware@8.3.0`
📦npm	`webpack-dev-middleware`	all versions	7.4.6`npm install webpack-dev-middleware@7.4.6`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for webpack-dev-middleware, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update webpack-dev-middleware to 8.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-76844 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

A path traversal flaw exists in webpack-dev-middleware when resolving URLs using a publicPath configuration lacking a trailing slash. By supplying a crafted URL with improper dot-dot positioning within a segment, an attacker can bypass the path traversal validation guard and offset calculation. When backed by a…

Workaround published by Red Hat

Ensure that the configured publicPath always ends with a trailing slash (e.g., '/assets/'), or utilize the default setting ('auto'), which resolves to '/' and is unmitigated by default. Alternatively, avoid backing the middleware with a physical filesystem (writeToDisk: false).

Source: Red Hat security advisory for CVE-2026-76844 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Data Grid 8.6.3	`redhat-datagrid-maven-repository.zip`	RHSA-2026:69296
Red Hat Discovery 2	`discovery/discovery-ui-rhel9:1788206196`	RHSA-2026:61783
Red Hat Migration Toolkit 1.8	`rhmtc/openshift-migration-ui-rhel8:1789546373`	RHSA-2026:68681

Frequently Asked Questions

> [!IMPORTANT] > CVE-2026-76844 was assigned and published for this issue by VulnCheck on 2026-08-24 without prior coordination with the webpack maintainers or the OpenJS Foundation, which holds the CVE Numbering Authority scope for webpack projects. Neither the maintainers nor the OpenJS CNA were notified before publication, and no fix was available at that time. This advisory is the coordinated record produced by the webpack maintainers and the OpenJS Foundation CNA. ### Impact `webpack-dev-middleware` resolves a request to a local file in `getFilenameFromUrl`. When the configured `publicP

O3 Security · Impact-Aware SCA

Is CVE-2026-76844 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works