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CVE-2026-11856 curl CVE debrief

CVE-2026-11856 is a critical vulnerability in libcurl that wrongly passes on the `Authorization:` header field. This occurs when using libcurl to do a transfer to a specific HTTP origin and then changing the origin for a second transfer, reusing the same handle. The vulnerability has a CVSS score of 9.8 and is classified as CRITICAL. Users of libcurl, particularly those using Digest authentication, should be aware of this vulnerability and take steps to mitigate it.

Vendor
curl
Product
Unknown
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-03
Original CVE updated
2026-09-15
Advisory published
2026-07-03
Advisory updated
2026-09-15

Who should care

Users of libcurl, particularly those using Digest authentication, should be aware of this vulnerability and take steps to mitigate it. This includes reviewing and updating libcurl configurations, monitoring for suspicious activity, and applying the patch provided by the vendor. Operators, platform administrators, vulnerability management teams, and security teams should review the official advisory and CVE record to validate the information and plan for potential mitigations.

Technical summary

The vulnerability is caused by libcurl wrongly passing on the `Authorization:` header field meant for one HTTP origin to another. This can occur when reusing the same handle for multiple transfers. The affected product is libcurl, and the vulnerability has a high impact on confidentiality, integrity, and availability. Defenders should review the official advisory and CVE record to validate the information and plan for potential mitigations.

Defensive priority

High

Recommended defensive actions

  • Apply the patch provided by the vendor
  • Review and update libcurl configurations
  • Monitor for suspicious activity
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-03T07:16:23.973Z and was last modified on 2026-07-07T19:43:55.600Z. The source details are limited, and further verification is needed to confirm the affected scope and severity. Defenders should review the official advisory and CVE record to validate the information and plan for potential mitigations.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-11856 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-11856

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-11856 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-11856

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://curl.se/docs/CVE-2026-11856.html

    2499f714-1537-4658-8207-48ae4bb9eae9 - Patch, Vendor Advisory

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://curl.se/docs/CVE-2026-11856.json

    2499f714-1537-4658-8207-48ae4bb9eae9 - Vendor Advisory

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://hackerone.com/reports/3793260

    2499f714-1537-4658-8207-48ae4bb9eae9 - Exploit, Issue Tracking, Third Party Advisory

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.