CVE-2026-6253
proxy credentials leak over redirect-to proxy
A public proof of concept exists; no exploitation attested.
- Published2026-05-13
- Fixed in8.20.0
- WeaknessCWE-522
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « 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
curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen when the following conditions are true: 1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy
Timeline
dates in UTC- 2026-05-1313:01CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-6253?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-6253?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 8.20 | ≥ 7.14.1, < 8.20.0 | 8.20.0 | NVD |
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_2.7and 3 other packages
Vendor advisories
curl: curl: Proxy credential disclosure via redirects to unauthenticated proxies
build-of-trustee/trustee-rhel9 as a component of Confidential Compute Attestation · confidential-compute-attestation-tech-preview/trustee-rhel9 as a component of Confidential Compute Attestation · openshift-sandboxed-containers/osc-operator-bundle as a component of Confidential Compute Attestation · +36 more
Red Hat Security Advisory: Red Hat Cost Management On-Premise container image update
Red Hat Security Advisory: curl security update
Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.62 SP5 security update
Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update
Fix
- Update Haxx curl to 8.20.0
- Vendor fix Red Hat Product Security RHSA-2026:87400 · 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.
- Vendor fix Red Hat Product Security RHSA-2026:80512 · 49 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
- Vendor fix Red Hat Product Security RHSA-2026:56869 · 1 productBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
- Vendor fix Red Hat Product Security RHSA-2026:12916 · 9 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
- Workaround from the vendor Red Hat Product Security RHSA-2026:87400 · 1 productTo mitigate this issue, avoid configuring curl or libcurl to use proxies that require credentials. This prevents the scenario where credentials for a first proxy could be inadvertently passed to a second proxy during a redirect.
- No fix available, says the vendor Red Hat Product Security CVE-2026-6253 · 30 productsFix deferred
Advisories and patches
- curl.sePatch · Vendor Advisory
- curl.seVendor Advisory
- www.openwall.comPatch
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 decisionpoc2026-05-13
- OpenCVESSVC decisionpoc—
- CISA-ADPCVSS 3.15.92026-05-13
- CNAweakness (CWE)CWE-522read 2026-10-23
- NVDweakness (CWE)CWE-522read 2026-10-23
- FIRST EPSSEPSS score0.7 %2026-10-23
- OSVaffected packages—
- Microsoft MSRCadvisory—
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- Published
- 2026-05-13
- Last Modified
- 2026-09-15
- NVD status
- Modified
- MSRC Title
- proxy credentials leak over redirect-to proxy
Frequently asked questions
What is CVE-2026-6253?
Is CVE-2026-6253 actively exploited?
What is the CVSS score for CVE-2026-6253?
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Same product first, then the same vendor advisory and the same publication week.