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Public proof of conceptFix available

CVE-2026-11856

A public proof of concept exists; no exploitation attested.

  • Published2026-07-03
  • Fixed in8.21.0
  • WeaknessCWE-294

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

Successfully 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`.

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-2026-11856?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-11856?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
8.21≥ 7.10.6, < 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.

Packages

  • libcurlAlmaLinux:10all versions · fixed in 8.12.1-4.el10_2.6and 3 other packages
  • libcurlAlmaLinux:9all versions · fixed in 7.76.1-40.el9_8.8and 4 other packages

Vendor advisories

  • CVE-2026-11856 Red Hat Product Security227 products fixed · 15 known affected

    curl: curl: Information disclosure via incorrect Digest authentication header reuse

    curl as a component of Red Hat Enterprise Linux 6 · curl.src as a component of Red Hat Enterprise Linux 6 · libcurl as a component of Red Hat Enterprise Linux 6 · +12 more

  • RHSA-2026:82939 Red Hat Product Security5 products fixed

    Red Hat Security Advisory: Red Hat Update Infrastructure 5.3 security update

  • RHSA-2026:80511 Red Hat Product Security74 products fixed

    Red Hat Security Advisory: curl security update

  • RHSA-2026:79357 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Cost Management On-Premise container image update

  • RHSA-2026:72506 Red Hat Product Security49 products fixed

    Red Hat Security Advisory: curl security update

  • RHSA-2026:69125 Red Hat Product Security49 products fixed

    Red Hat Security Advisory: curl security update

4 more advisories

Full record on NVD

Fix

  1. Update Haxx curl to 8.21.0
  2. Vendor fix Red Hat Product Security RHSA-2026:82939 · 5 productsThe container images provided by this release, apart from the installer, should be deployed using rhui-installer utility. See the official documentation for more details.
  3. Vendor fix Red Hat Product Security RHSA-2026:80511 · 74 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  4. Vendor fix Red Hat Product Security RHSA-2026:79357 · 1 productThe container image provided by this update can be downloaded from the Red Hat container registry at registry.redhat.io using the "podman pull" command.
  5. Vendor fix CISA ICSA-26-293-05 · 2 productsUpdate to CMU Firmware version 13.9.1
  6. Vendor fix CISA ICSA-26-293-05 · 1 productUpdate to CMU Firmware version 13.9.1 or 13.7.9 (when available)
  7. Vendor fix CISA ICSA-26-293-05 · 1 productUpdate to CMU Firmware version 13.9.1 or 13.8.3*

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

  • CISA-ADPSSVC decisionpoc2026-07-06
  • OpenCVESSVC decisionpoc—
  • CISA-ADPCVSS 3.19.82026-07-06
  • CNAweakness (CWE)CWE-294read 2026-10-23
  • NVDweakness (CWE)CWE-294read 2026-10-23
  • FIRST EPSSEPSS score0.7 %2026-10-23
  • OSVaffected packages—

Technical details

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

Frequently asked questions

What is CVE-2026-11856?

Successfully 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`.

Is CVE-2026-11856 actively exploited?

A proof-of-concept exploit exists for CVE-2026-11856, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-11856?

CVE-2026-11856 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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