CVE-2026-6253

proxy credentials leak over redirect-to proxy

MEDIUM

5.9

CVSS Score

Published: May 13, 2026 at 08:28 AM UTC

Updated: September 15, 2026 at 07:35 AM UTC

1 product affected across 1 vendorCurl

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Severity

MEDIUM5.9

Exploit prediction

EPSS 0.7%

SSVC

PoC

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

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Curl · Haxx

95%

7.14.1 ≤ v < 8.14.27.14.1 ≤ v < 8.20.08.15.0 ≤ v < 8.16.18.17.0 ≤ v < 8.20.03b60bb725913ce7339aefef0a14b12df4c24db607.14.1 7.15.0 7.15.1 7.15.2 7.15.3 7.15.4 7.15.5 7.16.0 7.16.1 7.16.2 7.16.3 7.16.4 7.17.0 7.17.1 7.18.0 7.18.1 7.18.2 7.19.0 7.19.1 7.19.2 7.19.3 7.19.4 7.19.5 7.19.6 7.19.7 7.20.0 7.20.1 7.21.0 7.21.1 7.21.2 7.21.3 7.21.4 7.21.5 7.21.6 7.21.7 7.22.0 7.23.0 7.23.1 7.24.0 7.25.0 7.26.0 7.27.0 7.28.0 7.28.1 7.29.0 7.30.0 7.31.0 7.32.0 7.33.0 7.34.0 7.35.0 7.36.0 7.37.0 7.37.1 7.38.0 7.39.0 7.40.0 7.41.0 7.42.0 7.42.1 7.43.0 7.44.0 7.45.0 7.46.0 7.47.0 7.47.1 7.48.0 7.49.0 7.49.1 7.50.0 7.50.1 7.50.2 7.50.3 7.51.0 7.52.0 7.52.1 7.53.0 7.53.1 7.54.0 7.54.1 7.55.0 7.55.1 7.56.0 7.56.1 7.57.0 7.58.0 7.59.0 7.60.0 7.61.0 7.61.1 7.62.0 7.63.0 7.64.0 7.64.1 7.65.0 7.65.1 7.65.2 7.65.3 7.66.0 7.67.0 7.68.0 7.69.0 7.69.1 7.70.0 7.71.0 7.71.1 7.72.0 7.73.0 7.74.0 7.75.0 7.76.0 7.76.1 7.77.0 7.78.0 7.79.0 7.79.1 7.80.0 7.81.0 7.82.0 7.83.0 7.83.1 7.84.0 7.85.0 7.86.0 7.87.0 7.88.0 7.88.1 8.0.0 8.0.1 8.1.0 8.1.1 8.1.2 8.10.0 8.10.1 8.11.0 8.11.1 8.12.0 8.12.1 8.13.0 8.14.0 8.14.1 8.15.0 8.16.0 8.17.0 8.18.0 8.19.0 8.2.0 8.2.1 8.3.0 8.4.0 8.5.0 8.6.0 8.7.0 8.7.1 8.8.0 8.9.0 8.9.1

Vendor states this is fixed in 188c2f166a20fa97c2325b2da7d0e5cecc13725f (fixed)

Affected range stops below 8.14.2, so it looks safe — our inference, not a vendor statement

Affected range stops below 8.16.1, so it looks safe — our inference, not a vendor statement

Affected range stops below 8.20.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (4)

Vendor Advisory

Source: cverecord

https://curl.se/docs/CVE-2026-6253.json

PatchVendor Advisory

Source: cverecord

https://curl.se/docs/CVE-2026-6253.html

ExploitIssue TrackingThird Party Advisory

Source: cverecord

https://hackerone.com/reports/3669637

Mailing ListPatchThird Party Advisory

Source: af854a3a-2127-422b-91ae-364da2661108

http://www.openwall.com/lists/oss-security/2026/04/29/11

SSVC — Action Prioritization

SSVCPoCNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.9MEDIUMCISA-ADP

Attack Vector: NETWORK
Complexity: HIGH
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: HIGH

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-522

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