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Noroxi
NVD / CVE Program· CNA curl

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

Noroxi assessment

Priority: Monitor (action score 23/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.71% (FIRST EPSS); higher than 54% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: curl curl 188c2f166a20fa97c2325b2da7d0e5cecc13725f, 8.14.2, 8.16.1; azl3 cmake 3.30.3-13 on Azure Linux 3.0 3.30.3-14; azl3 curl 8.11.1-7 on Azure Linux 3.0 8.11.1-8.

Low priority for now. Upgrade to curl curl 188c2f166a20fa97c2325b2da7d0e5cecc13725f, 8.14.2, 8.16.1; azl3 cmake 3.30.3-13 on Azure Linux 3.0 3.30.3-14; azl3 curl 8.11.1-7 on Azure Linux 3.0 8.11.1-8 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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

MediumCVSS 5.9 · v3.1—No exploit Fix available
Published
May 13, 2026
Updated
Sep 15, 2026
EPSS
0.7% · 54th percentile

Report tools

JSON

Action score

23

Monitor

Low priority for now.

CVSS
23 / 40 · 5.9 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.7%

CISA SSVC decision

Exploitation
proof of concept
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-6253

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
haxxcurl

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • haxx curl7.14.1 and later · before 8.20.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (curl). Independent of NVD's CPE analysis and usually ahead of it.

  • curl curl

    • 8.19.0, 8.18.0, 8.17.0, 8.16.0, 8.15.0, 8.14.1, 8.14.0, 8.13.0, 8.12.1, 8.12.0, 8.11.1, 8.11.0 … (+24)affected
    • 7.14.1 and later · before 8.14.2affected · semver
    • 8.15.0 and later · before 8.16.1affected · semver
    • 8.17.0 and later · before 8.20.0affected · semver
    • 3b60bb725913ce7339aefef0a14b12df4c24db60 and later · before 188c2f166a20fa97c2325b2da7d0e5cecc13725faffected · git

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10curlbefore 8.12.1-4.el10_2.78.12.1-4.el10_2.7
AlmaLinux:10libcurlbefore 8.12.1-4.el10_2.78.12.1-4.el10_2.7
AlmaLinux:10libcurl-develbefore 8.12.1-4.el10_2.78.12.1-4.el10_2.7
AlmaLinux:10libcurl-minimalbefore 8.12.1-4.el10_2.78.12.1-4.el10_2.7
Alpine:v3.21curlfrom 7.14.1 · before 8.14.1-r38.14.1-r3
Alpine:v3.22curlfrom 7.14.1 · before 8.14.1-r48.14.1-r4
Alpine:v3.23curlfrom 7.14.1 · before 8.20.0-r08.20.0-r0
Debian:12curlfrom 0—
Debian:13curlbefore 8.14.1-2+deb13u48.14.1-2+deb13u4
Debian:14curlbefore 8.20.0~rc3-18.20.0~rc3-1
openSUSE:Leap 16.0curlbefore 8.14.1-160000.6.18.14.1-160000.6.1
openSUSE:Tumbleweedcurlbefore 8.20.0-1.18.20.0-1.1
Red Hat:enterprise_linux:10.2curlbefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2curl-debuginfobefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2curl-debugsourcebefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2libcurlbefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2libcurl-debuginfobefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2libcurl-develbefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2libcurl-minimalbefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:enterprise_linux:10.2libcurl-minimal-debuginfobefore 0:8.12.1-4.el10_2.70:8.12.1-4.el10_2.7
Red Hat:hummingbird:1curlbefore 0:8.20.0-0.1.hum10:8.20.0-0.1.hum1
Red Hat:hummingbird:1libcurlbefore 0:8.20.0-0.1.hum10:8.20.0-0.1.hum1
Red Hat:hummingbird:1libcurl-develbefore 0:8.20.0-0.1.hum10:8.20.0-0.1.hum1
Red Hat:hummingbird:1libcurl-minimalbefore 0:8.20.0-0.1.hum10:8.20.0-0.1.hum1

+5

Same product

haxx: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-22901curl 7.75.0 through 7.76.1 suffers from a use-after-free vulnerability resulting in already freed memory being used when a TLS 1.3 session t
    51Plan
  • CVE-2023-38039When curl retrieves an HTTP response, it stores the incoming headers so that they can be accessed later via the libcurl headers API.
    47Plan
  • CVE-2024-2398HTTP/2 push headers memory-leak
    45Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-5545May 13, 2026 · wrong reuse of HTTP Negotiate connection
    26Monitor
  • ← EarlierCVE-2026-5773May 13, 2026 · wrong reuse of SMB connection
    30Monitor
  • Later →CVE-2026-6276May 13, 2026 · stale custom cookie host causes cookie leak
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
curl curl188c2f166a20fa97c2325b2da7d0e5cecc13725fVendor (CNA)
curl curl8.14.2Vendor (CNA)
curl curl8.16.1Vendor (CNA)
curl curl8.20.0Vendor (CNA)
azl3 cmake 3.30.3-13 on Azure Linux 3.03.30.3-14 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 curl 8.11.1-7 on Azure Linux 3.08.11.1-8 · CBL-Mariner ReleasesMicrosoft (MSRC)
almalinux:curl8.12.1-4.el10_2.7 · AlmaLinux:10Package registry (OSV)
almalinux:libcurl8.12.1-4.el10_2.7 · AlmaLinux:10Package registry (OSV)
almalinux:libcurl-devel8.12.1-4.el10_2.7 · AlmaLinux:10Package registry (OSV)
almalinux:libcurl-minimal8.12.1-4.el10_2.7 · AlmaLinux:10Package registry (OSV)
alpine:curl8.14.1-r3 · Alpine:v3.21Package registry (OSV)
alpine:curl8.20.0-r0 · Alpine:v3.23Package registry (OSV)
debian:curl8.14.1-2+deb13u4 · Debian:13Package registry (OSV)
opensuse:curl8.20.0-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:curl0:8.20.0-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:curl-debuginfo0:8.12.1-4.el10_2.7 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:curl-debugsource0:8.12.1-4.el10_2.7 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:libcurl0:8.20.0-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libcurl-debuginfo0:8.12.1-4.el10_2.7 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:libcurl-devel0:8.20.0-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libcurl-minimal0:8.20.0-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libcurl-minimal-debuginfo0:8.12.1-4.el10_2.7 · Red Hat:enterprise_linux:10.2Package registry (OSV)
rocky linux:curl0:8.12.1-4.el10_2.7 · Rocky Linux:10Package registry (OSV)
suse:curl8.14.1-160000.6.1 · SUSE:Linux Micro 6.2Package registry (OSV)
suse:curl-mini8.14.1-160000.6.1 · SUSE:Linux Enterprise Server 16.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-907951 days apartstale proxy password leak
    39Monitor
  • CVE-2026-892651 days apartpassword leak with netrc and user in URL
    36Monitor
  • CVE-2026-378363 days aparttoken leak with redirect and netrc
    21Monitor
  • CVE-2025-14524125 days apartbearer token leak on cross-protocol redirect
    21Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-522 · Insufficiently Protected Credentials

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records