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PatchSiren cyber security CVE debrief

CVE-2026-8927 Haxx CVE debrief

libcurl fails to clear proxy authentication state between requests when reusing a handle for sequential transfers driven by environment-variable proxy configuration. 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`. This issue can lead to unintended security risks in certain scenarios, particularly for applications that rely on sequential transfers with different proxy configurations.

Vendor
Haxx
Product
Curl
CVSS
CRITICAL 9.1
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 in applications that rely on sequential transfers with different proxy configurations, especially those using Digest authentication. Developers and administrators should assess the impact on their applications and take necessary actions to mitigate the vulnerability. This includes reviewing and updating applications that use libcurl, implementing additional monitoring and logging, and considering alternative libraries or workarounds.

Technical summary

The libcurl library fails to properly reset the proxy authentication state when reusing a handle for subsequent transfers with different proxy configurations. This can lead to unintended leakage of Proxy-Authorization headers across different proxies, potentially causing security issues in certain scenarios. The vulnerability is particularly concerning for applications that use libcurl for sequential transfers with different proxy settings. Developers and administrators should assess the impact on their applications and take necessary actions to mitigate the vulnerability.

Defensive priority

High

Recommended defensive actions

  • Update libcurl to the latest version that fixes the vulnerability
  • Review and update applications that use libcurl for sequential transfers with different proxy configurations
  • Implement additional monitoring and logging to detect potential misuse of Proxy-Authorization headers
  • Consider using alternative libraries or workarounds that do not rely on libcurl handle reuse
  • 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

Evidence notes

The CVE record was published on 2026-07-03T07:16:25.123Z and was last modified on 2026-07-07T23:21:03.530Z. The NVD entry is currently Analyzed. This information is based on the provided source corpus and may not reflect additional details not included in the corpus. Further verification is recommended.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-8927 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-8927

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

  • CVE-2026-8927 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-8927

    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-2026-8927.html

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

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://curl.se/docs/CVE-2026-8927.json

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

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://hackerone.com/reports/3744543

    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.