CurlApplication · Haxx
CVE-2026-11856
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedSuccessfully 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`.
In the news
Third-party coverageSurfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceWhen libcurl handles are reused across different HTTP origins with Digest authentication, the Authorization header from the first transfer is incorrectly reused for subsequent transfers to different hosts. This causes authentication credentials meant for one origin (hostA) to be sent to another origin (hostB), resulting in credential leakage.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
CurlApplication
>= 7.10.6, < 8.21.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed libcurl versionRun 'curl --version' to display version information, or check the libcurl library file (e.g., 'ldd /path/to/binary' or 'pkg-config --modversion libcurl')Affected if Version is greater than or equal to 7.10.6 AND less than 8.21.0
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Identify Digest authentication usage in application codeSearch source code for 'CURLOPT_DIGEST' or 'CURLOPT_USERPWD' or check application configuration for HTTP authentication methods using DigestAffected if Application uses libcurl with Digest authentication enabled via CURLOPT_DIGEST or implicitly via Digest-compatible auth settings
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Detect handle reuse patterns across originsReview application code for patterns where a CURL handle is created once and reused across multiple requests to different hostnames (e.g., a global or persistent curl handle used for multiple API calls)Affected if Application reuses the same CURL* handle for requests to different hosts/origins with Digest authentication enabled
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Verify cross-origin request patternsAnalyze network logs or application flow to confirm requests go to multiple different origins (different hostnames or domains) using the same reused handle with Digest authAffected if Requests to different origins (hostA, hostB, etc.) share a single curl handle that retains the Authorization header from the first request
You are affected if your libcurl version is >= 7.10.6 and < 8.21.0 AND your application reuses curl handles across different origins while using Digest authentication, causing credentials from one host to be sent to another.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped8.21.0
Avoid reusing libcurl handles across different origins when using Digest authentication, or implement explicit header clearing between transfers to different hosts.
curl/libcurl 8.21.0 or later
- 1. Identify the current curl/libcurl version in use by running `curl --version` or checking library version in your application.
- 2. If the version is >= 7.10.6 and < 8.21.0, plan for an upgrade to version 8.21.0 or later.
- 3. Download the latest curl release from the official source: https://curl.se/download.html
- 4. For systems using package managers (apt, yum, brew, etc.), update via: `apt update && apt upgrade curl` (Debian/Ubuntu), `sudo yum update curl` (RHEL/CentOS), or `brew upgrade curl` (macOS).
- 5. For applications using libcurl, rebuild or update the linked libcurl library to version 8.21.0 or later.
- 6. After upgrading, verify the fix by testing the Digest authentication scenario: perform a transfer to hostA with Digest auth, then reuse the handle to transfer to hostB and confirm no Authorization header is sent to hostB.
- 7. Restart any services or applications that use curl/libcurl to ensure the new version is loaded.
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Curl
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-11856 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-11856 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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