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Fencer Vulns
medium 5.9

CVE-2023-27535 json

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature...

published 2023-03-30 3 y ago modified 2026-10-24 16 d ago also EUVD-2023-31290 , JLSEC-2025-31

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.8%
EPSS 1.8% chance of exploitation in 30 days, percentile 78%
public exploits
0
none known

Summary

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool for reuse if they match the current setup. However, certain FTP settings such as CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC, and CURLOPT_USE_SSL were not included in the configuration match checks, causing them to match too easily. This could lead to libcurl using the wrong credentials when performing a transfer, potentially allowing unauthorized access to sensitive information.

Patch / fix

  • julia CURL_jll 8.5.0+0
  • julia LibCURL_jll 8.0.1+0
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • curl Debian 14, Debian 13, Debian 12 7.88.1-7

debian advisories DEBIAN-CVE-2023-27535

  • curl Ubuntu 18.04 LTS 7.58.0-2ubuntu3.24
  • curl Ubuntu 20.04 LTS 7.68.0-1ubuntu2.18
  • curl Ubuntu 22.04 LTS 7.81.0-1ubuntu1.10
  • curl Ubuntu Pro 14.04 LTS 7.35.0-1ubuntu2.20+esm15
  • curl Ubuntu Pro 16.04 LTS 7.47.0-1ubuntu2.19+esm8

ubuntu advisories UBUNTU-CVE-2023-27535

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • curl RHEL 8 7.61.1-30.el8_8.2
  • libcurl RHEL 8 7.61.1-30.el8_8.2
  • libcurl-minimal RHEL 8 7.61.1-30.el8_8.2
  • curl RHEL 9 7.76.1-23.el9_2.1
  • libcurl RHEL 9 7.76.1-23.el9_2.1
  • curl-minimal RHEL 9 7.76.1-23.el9_2.1
  • libcurl-minimal RHEL 9 7.76.1-23.el9_2.1
  • curl RHEL 8.6 EUS 7.61.1-22.el8_6.12

red hat advisories RHSA-2024:0428RHSA-2023:3106RHSA-2023:2650

  • curl SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLES 12 SP4-ESPOS +2 more 7.60.0-4.56.1
  • curl SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLE High Performance Computing 15 SP1-LTSS +1 more 7.60.0-150000.51.1
  • curl SLE Real Time 15 SP3, SLE Micro 5.2, SLE Micro 5.1 7.66.0-150200.4.52.1
  • curl SLE Module for Basesystem 15 SP4, SLE Micro 5.3, openSUSE Leap Micro 5.3 +1 more 7.79.1-150400.5.18.1
  • curl SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 7.60.0-11.60.1

suse advisories SUSE-SU-2023:2228-1SUSE-SU-2023:2226-1SUSE-SU-2023:1711-1SUSE-SU-2023:1582-1SUSE-SU-2023:0865-1

  • curl openSUSE Tumbleweed 8.0.1-1.1

opensuse advisories openSUSE-SU-2024:12812-1

  • curl AlmaLinux 8 7.61.1-30.el8_8.2
  • libcurl AlmaLinux 8 7.61.1-30.el8_8.2
  • libcurl-minimal AlmaLinux 8 7.61.1-30.el8_8.2
  • curl AlmaLinux 9 7.76.1-23.el9_2.1
  • libcurl AlmaLinux 9 7.76.1-23.el9_2.1
  • curl-minimal AlmaLinux 9 7.76.1-23.el9_2.1
  • libcurl-minimal AlmaLinux 9 7.76.1-23.el9_2.1

almalinux advisories ALSA-2023:3106ALSA-2023:2650

  • curl Rocky Linux 8 7.61.1-30.el8_8.2

rocky linux advisories RLSA-2023:3106

  • curl Alpine 3.16, Alpine 3.15, Alpine 3.14 8.0.1-r0
  • curl Alpine 3.17 7.88.1-r1
  • curl Alpine 3.24, Alpine 3.23, Alpine 3.22 +4 more 8.0.0-r0

alpine advisories ALPINE-CVE-2023-27535

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • cmake CBL-Mariner 2.0 3.21.4-13
  • mysql CBL-Mariner 2.0 8.0.34-1
  • rust CBL-Mariner 2.0 1.72.0-2
  • curl CBL-Mariner 2.0 8.0.1-1
  • cmake Azure Linux 3.0 3.28.2-1
  • tensorflow Azure Linux 3.0 2.16.1-1

azure linux advisories AZL-25787AZL-25805AZL-25811AZL-25846AZL-34611AZL-38512

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-27535 updated cvss 5.9

curl: FTP too eager connection reuse

  • Red Hat .NET Core 3.1 on Red Hat Enterprise Linux rh-dotnet31-curl, rh-dotnet31-libcurl Red Hat Enterprise Linux 6 curl, libcurl
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 curl, libcurl
    affected: no fix planned “Will not fix”
  • Red Hat JBCS httpd 2.4.51.sp2
    fixed: vendor fix RHSA-2023:3355
  • Red Hat Enterprise Linux AppStream (v. 9) libcurl-devel 7.76.1-23.el9_2.1, curl-debuginfo 7.76.1-23.el9_2.1, curl-debugsource 7.76.1-23.el9_2.1, libcurl-debuginfo 7.76.1-23.el9_2.1, curl-minimal-debuginfo 7.76.1-23.el9_2.1, libcurl-minimal-debuginfo 7.76.1-23.el9_2.1
    fixed: vendor fix RHSA-2023:2650
  • Red Hat Enterprise Linux BaseOS (v. 8) curl 7.61.1-30.el8_8.2, libcurl 7.61.1-30.el8_8.2, libcurl-minimal 7.61.1-30.el8_8.2
    fixed: vendor fix RHSA-2023:3106
  • Red Hat Enterprise Linux BaseOS (v. 9) curl 7.76.1-23.el9_2.1, libcurl 7.76.1-23.el9_2.1, curl-minimal 7.76.1-23.el9_2.1, libcurl-minimal 7.76.1-23.el9_2.1
    fixed: vendor fix RHSA-2023:2650
  • Red Hat Enterprise Linux BaseOS EUS (v.8.6) curl 7.61.1-22.el8_6.12, libcurl 7.61.1-22.el8_6.12, libcurl-minimal 7.61.1-22.el8_6.12
    fixed: vendor fix RHSA-2024:0428

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 5.9

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-24-046-11 updated cvss 5.9

Siemens SCALANCE XCM-/XRM-300

  • Siemens SCALANCE XCH328 (6GK5328-4TS01-2EC2) <V2.4 Siemens SCALANCE XCM324 (6GK5324-8TS01-2AC2) <V2.4 Siemens SCALANCE XCM328 (6GK5328-4TS01-2AC2) <V2.4 Siemens SCALANCE XCM332 (6GK5332-0GA01-2AC2) <V2.4 Siemens SCALANCE XRH334 (24 V DC, 8xFO, CC) (6GK5334-2TS01-2ER3) <V2.4 Siemens SCALANCE XRM334 (2x230 V AC, 8xFO) (6GK5334-2TS01-4AR3) <V2.4
    +5 more products
    Siemens SCALANCE XRM334 (2x230 V AC, 12xFO) (6GK5334-3TS01-4AR3) <V2.4 Siemens SCALANCE XRM334 (24 V DC, 8xFO) (6GK5334-2TS01-2AR3) <V2.4 Siemens SCALANCE XRM334 (24 V DC, 12xFO) (6GK5334-3TS01-2AR3) <V2.4 Siemens SCALANCE XRM334 (230 V AC, 8xFO) (6GK5334-2TS01-3AR3) <V2.4 Siemens SCALANCE XRM334 (230 V AC, 12xFO) (6GK5334-3TS01-3AR3) <V2.4
    affected: fixed in V2.4 support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
17 mo ago

Exploit prediction

1.80% chance of exploitation in the next 30 days, higher than 78% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • hackerone.com https://hackerone.com/reports/1892780 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia CURL_jll
<8.5.0+0
8.5.0+0
julia LibCURL_jll
<8.0.1+0
8.0.1+0

Affected products

  • n/a https://github.com/curl/curl
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness
  • CWE-305 Authentication Bypass by Primary Weakness
  • CWE-287 Improper Authentication

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.