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Public proof of conceptFix available

CVE-2026-9546

A public proof of concept exists; no exploitation attested.

  • Published2026-07-03
  • Fixed in8.21.0
  • WeaknessCWE-200

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A vulnerability in libcurl caused the HTTP `Referer:` header to persist even when explicitly cleared. While the documentation states that passing NULL to `CURLOPT_REFERER` suppresses the header, the option failed to clear the internal state. As a result, the previous referrer string was erroneously reused and sent in subsequent requests, potentially leaking sensitive information to unintended servers.

Timeline

dates in UTC
  1. 2026-07-0307:16CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-9546?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-9546?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Haxx curl
BranchAffectedFixed in
8.x≥ 8.18.0, < 8.21.08.21.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-9546 Red Hat Product Security48 products fixed · 34 known affected

    libcurl: libcurl: Information disclosure due to persistent Referer header

    build-of-trustee/trustee-rhel9 as a component of Confidential Compute Attestation · openshift-sandboxed-containers/osc-podvm-payload-rhel9 as a component of Confidential Compute Attestation · curl as a component of Red Hat Enterprise Linux 10 · +31 more

  • RHSA-2026:34975 Red Hat Product Security39 products fixed

    Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

  • RHSA-2026:29017 Red Hat Product Security9 products fixed

    Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Full record on NVD

Fix

  1. Update Haxx curl to 8.21.0
  2. Vendor fix Red Hat Product Security CVE-2026-9546 · 39 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
  3. Workaround from the vendor Red Hat Product Security CVE-2026-9546 · 82 productsMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
  4. No fix available, says the vendor Red Hat Product Security CVE-2026-9546 · 34 productsAffected

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Published
2026-07-03
Last Modified
2026-09-15
NVD status
Modified

Frequently asked questions

What is CVE-2026-9546?

A vulnerability in libcurl caused the HTTP `Referer:` header to persist even when explicitly cleared. While the documentation states that passing NULL to `CURLOPT_REFERER` suppresses the header, the option failed to clear the internal state. As a result, the previous referrer string was erroneously reused and sent in subsequent requests, potentially leaking sensitive information to unintended servers.

Is CVE-2026-9546 actively exploited?

A proof-of-concept exploit exists for CVE-2026-9546, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-9546?

CVE-2026-9546 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

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