# CVE-2026-11856: cross-origin Digest auth state leak

> libcurl leaks Digest authentication headers to unintended hosts when reusing handles, potentially exposing credentials to attackers.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 3 Jul 2026
- **Updated:** 15 Sep 2026
- **Also known as:** ALPINE-CVE-2026-11856, AZL-91803, AZL-91830, BELL-CVE-2026-11856, CLSA-2026-1783703539, CLSA-2026-1783705168, CLSA-2026-1783937591, CLSA-2026-1783937768, CLSA-2026-1783937975, CLSA-2026-1783942033, CLSA-2026-1784123512, CURL-CVE-2026-11856, DEBIAN-CVE-2026-11856, ECHO-895d-0fcf-45bd, GHSA-9crq-qh8v-6xmm, JLSEC-2026-1201, MINI-mhj4-jp68-cpm2, MINI-pmx3-xcpx-8ggp, ROOT-OS-ALPINE-315-CVE-2026-11856, ROOT-OS-ALPINE-320-CVE-2026-11856, ROOT-OS-ALPINE-321-CVE-2026-11856, ROOT-OS-ALPINE-322-CVE-2026-11856, ROOT-OS-DEBIAN-11-CVE-2026-11856, ROOT-OS-DEBIAN-12-CVE-2026-11856, ROOT-OS-DEBIAN-13-CVE-2026-11856, UBUNTU-CVE-2026-11856

## What is CVE-2026-11856?

CVE-2026-11856 is a critical vulnerability in Haxx Curl, published on 3 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Successfully using libcurl to do a transfer to a specific HTTP origin
(`hostA`) with **Digest** authentication and then changing the origin to a
different one (`hostB`) for a second transfer, reusing the same handle, makes
libcurl wrongly pass on the `Authorization:` header field meant for `hostA`,
to `hostB`.

Weakness: CWE-294 (Authentication Bypass by Capture-replay)

## Which versions are affected by CVE-2026-11856?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2026-11856?

Upgrade to a fixed version.

## Is CVE-2026-11856 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-11856 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-2026-8925](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)
- [CVE-2016-4606](https://insights.sbomify.com/CVE-2016-4606/): Code injection in curl (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-11856 and fix it if it is affected.

What it is: CVE-2026-11856 is a critical vulnerability in Haxx Curl, published on 3 Jul 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-2026-11856 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-2026-11856/ (Markdown: https://insights.sbomify.com/CVE-2026-11856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-11856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-11856
- OSV: https://osv.dev/vulnerability/CVE-2026-11856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-11856/
Summaries are generated and may contain mistakes; the official description above is the record.