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CVE-2026-8927 — curl

CRITICAL

CVE-2026-8927 is a critical-severity (CVSS 9.1) CWE-294 vulnerability. A fix is available — see the affected versions and patch details below.

env-set cross-proxy Digest auth state leak

Also known asCURL-CVE-2026-8927
Published
Updated
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-8927.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk
0.00%0.33%0.67%1.00%0.4%0.5%0.5%0.5%Aug 26Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-8927 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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.

Affected Products

1 product · 1 configurations
Application
curlhaxx
≥ 7.12.0 && < 8.21.0
range

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Fix

    Upgrade the affected component to the fixed release for CVE-2026-8927, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This Important information disclosure vulnerability in libcurl arises when a handle is reused for sequential transfers with environment-variable proxy configurations, failing to clear the proxy authentication state. This oversight can lead to `Proxy-Authorization` headers being inadvertently sent to an incorrect…

Workaround published by Red Hat
To mitigate this issue, applications utilizing libcurl should avoid reusing handles when switching between different proxy configurations. This operational control prevents the unintended leakage of `Proxy-Authorization` headers to incorrect proxies.
Source: Red Hat security advisory for CVE-2026-8927 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Enterprise Linux 10curl-0:8.12.1-4.el10_2.4RHSA-2026:55432
Red Hat Enterprise Linux 10.0 Extended Update Supportcurl-0:8.12.1-1.el10_0.10RHSA-2026:72506
Red Hat Enterprise Linux 9curl-0:7.76.1-40.el9_8.7RHSA-2026:69126
Red Hat JBoss Core Services 2.4.62.SP5libcurl-1.dllRHSA-2026:56869
Cert Manager support for Red Hat OpenShift release 1.20cert-manager/jetstack-cert-manager-rhel9:1790223279RHSA-2026:72394
Cert Manager support for Red Hat OpenShift release 1.20cert-manager/cert-manager-istio-csr-rhel9:1790223719RHSA-2026:72395
Cert Manager support for Red Hat OpenShift release 1.20cert-manager/cert-manager-operator-rhel9:1790272426RHSA-2026:72399
Cert Manager support for Red Hat OpenShift release 1.20cert-manager/jetstack-cert-manager-acmesolver-rhel9:1790589998RHSA-2026:72470
UbuntuCRITICAL
USN-8487-1UbuntuUSN-8820-1Ubuntu

Frequently Asked Questions

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`.
O3 Security · Impact-Aware SCA

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CVE-2026-8927: curl (Critical 9.1)