dbcve.org
CurlApplication · Haxx

CVE-2026-8927

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
When reusing a libcurl handle for sequential transfers driven by environment-variable proxy configuration, libcurl fails to clear the proxy authentication state between requests. Specifically, if the initial transfer authenticates against `proxyA` using Digest auth, a subsequent transfer routed through `proxyB` erroneously leaks the `Proxy-Authorization:` header intended solely for `proxyA`.

In the news

Third-party coverage
Trending covered by 1 outlet this week · latest 1mo ago

Surfaced 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 · high confidence

When reusing a libcurl handle for sequential transfers using environment-variable proxy configuration, libcurl fails to clear proxy authentication state between requests. If the initial transfer authenticates to proxyA using Digest auth, subsequent transfers routed through proxyB erroneously leak the Proxy-Authorization header intended only for proxyA, causing credential disclosure to unintended proxy servers.

MitigationAvoid reusing libcurl handles across different proxy configurations, or explicitly clear authentication state between requests. Monitor for credential leakage to unauthorized proxies. Apply vendor patches when available.

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:>= 7.12.0, < 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. Check installed libcurl version
    Run `curl --version` to display version information, or programmatically check via `curl_version()` API
    Affected if Version is greater than or equal to 7.12.0 AND less than 8.21.0
  2. Verify proxy environment variables are set
    Inspect environment variables HTTP_PROXY, HTTPS_PROXY, ALL_PROXY (and lowercase variants) using `env | grep -i proxy` or `printenv`
    Affected if Any proxy-related environment variables are set to a non-empty value
  3. Identify curl handle reuse pattern in application
    Review application source code or runtime behavior for patterns where a curl easy handle is created once and used for multiple transfer operations
    Affected if Application reuses the same CURL handle across multiple requests without calling curl_easy_reset() or curl_easy_setopt(CURLOPT_PROXYAUTH, ...) between transfers
  4. Confirm proxy authentication is in use
    Check application code or logs for CURLOPT_PROXYAUTH, CURLOPT_PROXYUSERPWD options, or trace network traffic for Proxy-Authorization headers
    Affected if Application uses Digest, Basic, NTLM, or other proxy authentication methods
  5. Detect cross-proxy request scenario
    Monitor or log which proxy each request uses, checking if different proxy endpoints are accessed using the same handle over time
    Affected if The same curl handle is used to send requests through different proxy servers

You are affected if your curl version is >= 7.12.0 and < 8.21.0 AND you reuse curl handles across requests while using environment-variable-configured proxies with authentication, particularly when switching between different proxy servers.

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

Avoid reusing libcurl handles across different proxy configurations, or explicitly clear authentication state between requests. Monitor for credential leakage to unauthorized proxies. Apply vendor patches when available.

Recommended fix Moderate confidence

curl/libcurl 8.21.0 or later

  1. Identify all systems and applications using libcurl versions >= 7.12.0 and < 8.21.0
  2. Upgrade curl/libcurl to version 8.21.0 or later
  3. Verify the upgrade was successful by running 'curl --version' and confirming the version is >= 8.21.0
  4. If using libcurl programmatically, rebuild any applications that link against libcurl to ensure they use the updated library
Caveat Minor version upgrades in curl typically maintain backward compatibility, but review release notes for any API changes between your current version and 8.21.0

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

Fix this in Curl Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,960.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-8927 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-8927 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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