# CVE-2026-6276: stale custom cookie host causes cookie leak

> Attackers can steal cookies from a previous request when reusing a libcurl easy handle with a changed Host header.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 May 2026
- **Updated:** 15 Sep 2026
- **Also known as:** ALPINE-CVE-2026-6276, AZL-86655, AZL-86679, BELL-CVE-2026-6276, CLSA-2026-1785773934, CLSA-2026-1792808992, CURL-CVE-2026-6276, DEBIAN-CVE-2026-6276, ECHO-78b1-43ab-d59f, GHSA-2jc6-hc33-hv48, JLSEC-2026-1207, MINI-2256-qmv4-xpgc, MINI-9q6r-wh3r-gg9m, ROOT-OS-ALPINE-315-CVE-2026-6276, ROOT-OS-ALPINE-320-CVE-2026-6276, ROOT-OS-ALPINE-321-CVE-2026-6276, ROOT-OS-ALPINE-322-CVE-2026-6276, ROOT-OS-DEBIAN-11-CVE-2026-6276, ROOT-OS-DEBIAN-12-CVE-2026-6276, UBUNTU-CVE-2026-6276

## What is CVE-2026-6276?

CVE-2026-6276 is a high-severity vulnerability in Haxx Curl, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Using libcurl, when a custom `Host:` header is first set for an HTTP request
and a second request is subsequently done using the same *easy handle* but
without the custom `Host:` header set, the second request would use stale
information and pass on cookies meant for the first host in the second
request. Leak them.

Weakness: CWE-319 (Cleartext Transmission of Sensitive Information), CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-6276?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2026-6276?

Upgrade to a fixed version.

## Is CVE-2026-6276 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6276 exists.

## Other vulnerabilities in Haxx Curl

- [CVE-2026-19931](https://insights.sbomify.com/CVE-2026-19931/): Negotiate ambient user conn reuse (critical 9.8)
- [CVE-2026-10536](https://insights.sbomify.com/CVE-2026-10536/): HTTP/2 stream-dependency tree UAF (critical 9.8)
- [CVE-2026-11856](https://insights.sbomify.com/CVE-2026-11856/): cross-origin Digest auth state leak (critical 9.8)
- [CVE-2026-8925](https://insights.sbomify.com/CVE-2026-8925/): SASL double-free (critical 9.8)
- [CVE-2026-9079](https://insights.sbomify.com/CVE-2026-9079/): stale proxy password leak (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6276 and fix it if it is affected.

What it is: CVE-2026-6276 is a high-severity vulnerability in Haxx Curl, published on 13 May 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-2026-6276 exists.

Affected product: Haxx Curl. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-6276/ (Markdown: https://insights.sbomify.com/CVE-2026-6276/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6276
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6276
- OSV: https://osv.dev/vulnerability/CVE-2026-6276

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6276/
Summaries are generated and may contain mistakes; the official description above is the record.