CVE-2023-27535
MEDIUMEPSS 74th pctlDescription
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.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Exploit Intelligence
Elevated risk: more likely to be exploited than 74% of all known CVEs.
References
Related Vulnerabilities
Other CWE-305 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-31161 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2020-10923 | High | 8.8 | 85% | - | - |
| CVE-2023-28126 | Medium | 5.9 | 67% | - | - |
| CVE-2023-34124 | Critical | 9.8 | 46% | - | Fix |
| CVE-2025-32011 | Critical | 9.8 | 27% | - | - |
| CVE-2024-37085 | Medium | 6.8 | 26% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2023-27535?
Published advisories record a fix for 27 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2023-27535 being actively exploited?
Not that we know of. CVE-2023-27535 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 74% of all scored CVEs.
How severe is CVE-2023-27535?
CVE-2023-27535 has a CVSS v3 base score of 5.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2023-27535 affect?
Published advisories record a fix for curl (Debian), curl (Rocky), curl (Red Hat / RHEL), curl-debuginfo (Red Hat / RHEL), and 23 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-06-09.