CVE-2026-6253 | proxy credentials leak over redirect-to proxy

Exp

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

Published: 2026-05-13 Last update: 2026-05-14 Assigner: 2499f714-1537-4658-8207-48ae4bb9eae9 Source: 2499f714-1537-4658-8207-48ae4bb9eae9
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-6253 is rated Exploit Available (52.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.52%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-6253

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-6253

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 0.52% +0.50%
2 2026-05-13 — 0.02% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-6253

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-6253

GitHub Security Advisory for CVE-2026-6253

GHSA-6qjr-r96v-3wcx · Severity: medium — curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen...

OS Trackers for CVE-2026-6253

vendor priority summary link
debian not yet assigned CVE-2026-6253 not yet assigned priority: Debian including 1 source packages (curl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-6253
redhat medium — https://access.redhat.com/security/cve/CVE-2026-6253
suse medium CVE-2026-6253 severity moderate: SUSE including 8 source package names (curl-8.14.1-150400.5.83.1, curl-8.14.1-150600.4.43.1, …), 64 product×package rows across 19 product lines (SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS, SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, … (19 product lines)): First Fixed 64. https://www.suse.com/security/cve/CVE-2026-6253/
ubuntu medium CVE-2026-6253 medium priority: Ubuntu including 1 source packages (curl), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needed 4, released 4, pending 1. https://ubuntu.com/security/CVE-2026-6253

Affected software / configurations for CVE-2026-6253

Vendor Product Version Raw CPE
haxx curl >= 7.14.1, < 8.20.0 cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*

References for CVE-2026-6253

URL Tags
https://curl.se/docs/CVE-2026-6253.html Patch Vendor Advisory
https://curl.se/docs/CVE-2026-6253.json Vendor Advisory
https://hackerone.com/reports/3669637 Exploit Issue Tracking Third Party Advisory
http://www.openwall.com/lists/oss-security/2026/04/29/11 Mailing List Patch Third Party Advisory
cvelogic Threat Intelligence