dbcve.org
CurlApplication · Haxx

CVE-2026-11564

CRITICAL · 9.1 CVSS v3.1 Published 2026-07-03
Fix available
A fix is available. Upgrade to 8.21.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available 8 weeks old

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 · unedited
libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. An easy handle that first uses default native CA trust can continue trusting the native platform store after the application switches that same handle to custom CA material for a later transfer.

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 confidence

libcurl's connection pool retains the CA trust configuration from the initial request and incorrectly applies it to subsequent transfers using the same pooled connection. When an easy handle first performs a transfer with default native CA trust, then is reconfigured for custom CA material for a later transfer, the pooled connection still uses the original system CA store rather than the intended custom CA, potentially allowing MITM attacks.

MitigationEnsure connections are explicitly closed or handles are recreated when switching CA trust configurations between transfers, or avoid reusing easy handles across different CA configurations.

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
Affected:>= 8.17.0, < 8.21.0

CVSS 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
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify libcurl version
    Run 'curl --version' or check the libcurl library version installed on the system. On Linux, this may also be found via 'pkg-config --modversion libcurl' or by inspecting the shared library file (e.g., libcurl.so.4).
    Affected if The installed version is greater than or equal to 8.17.0 and less than 8.21.0
  2. Check for custom CA configuration usage
    Search code or configuration for usage of CURLOPT_CAINFO or CURLOPT_CAPATH options set via curl_easy_setopt(), which configure custom Certificate Authority certificates.
    Affected if Custom CA material is configured via CURLOPT_CAINFO or CURLOPT_CAPATH on any easy handle
  3. Identify easy handle reuse patterns
    Review code that performs multiple transfers using the same CURL easy handle. Look for instances where an easy handle is reused after initial transfer without being recreated.
    Affected if The same CURL easy handle is reused across multiple requests (this is the default connection pooling behavior)
  4. Verify CA configuration changes on reused handles
    Examine whether the same easy handle has different CURLOPT_CAINFO or CURLOPT_CAPATH values set at different points in the code execution, or if the handle is used with both default CA and custom CA configurations.
    Affected if An easy handle is first used with default CA trust and later reconfigured with custom CA (or vice versa) for a subsequent transfer on the same handle

A user is affected if they are running libcurl 8.17.0 through 8.20.x, reuse the same easy handle across multiple requests, and switch between default system CA store and custom CA configurations on that reused handle.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 8.21.0 or later
Fixed in 8.21.0
Vendor patch curl.se →
Interim mitigation

Ensure connections are explicitly closed or handles are recreated when switching CA trust configurations between transfers, or avoid reusing easy handles across different CA configurations.

Recommended fix High confidence

curl 8.21.0 or later

  1. Identify all systems running curl versions >= 8.17.0 and < 8.21.0 using 'curl --version' or package management tools
  2. Upgrade curl to version 8.21.0 or later via your system's package manager or from https://curl.se/download/
  3. Verify the upgrade was successful by running 'curl --version' and confirming the version number is 8.21.0 or higher
  4. Test any applications that use libcurl to ensure certificate validation now works correctly with custom CA material

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Curl Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-11564 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data