CVE-2023-27535 — An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse...
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 1.6% (30-day exploitation probability)+11
- Technical severity (medium)+3
- CISA SSVC: exploitation "poc"+5
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Fedoraproject Fedora, Haxx Libcurl…).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Debian | Debian Linux | version 10.0 | Vulnerable | NIST National Vulnerability Database |
| Fedoraproject | Fedora | version 36 | Vulnerable | NIST National Vulnerability Database |
| Haxx | Libcurl | ≥ 7.13.0 and ≤ 7.88.1 | Vulnerable | NIST National Vulnerability Database |
| Netapp | Active Iq Unified Manager | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | H300s Firmware | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | H410s Firmware | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | H500s Firmware | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | H700s Firmware | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Ontap 9 | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Splunk | Universal Forwarder | ≥ 8.2.0 and < 8.2.12≥ 9.0.0 and < 9.0.6version 9.1.0 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 5.9 | CVSS 3.1 | Medium | 2.2 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 5.9 | CVSS 3.1 | Medium | 2.2 | 3.6 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database |
| 5.9 | CVSS 3.1 | Medium | — | — | CISA-ADP via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.
Timeline
What happened to this CVE, newest first.
- 2026
- SSVC assessment updated
- Record published
- Affected products added · haxx/libcurl, fedoraproject/fedora, debian/debian linux, netapp/active iq unified manager, netapp/ontap 9, netapp/h300s
- CVSS changed · 5.9
- Source status changed · → Modified
- Record created in this database
- 2023
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
13 on the record
- security.netapp.com/advisory/ntap-20230420-0010/
- cert-portal.siemens.com/productcert/html/ssa-806742.html
- github.com/advisories/GHSA-q9fm-68jc-87x3
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/36NBD5
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/36NB
- hackerone.com/reports/1892780
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/36NB
- cert-portal.siemens.com/productcert/html/ssa-943925.html
- security.netapp.com/advisory/ntap-20230420-0010
- nvd.nist.gov/vuln/detail/CVE-2023-27535
- lists.debian.org/debian-lts-announce/2023/04/msg00025.html
- security.gentoo.org/glsa/202310-12
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-12996 A use-after-free in OpenVPN 2.6.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 allows remote... Jul 30, 2026
- High CVE-2026-22049 Authentication Bypass Using an Alternate Path or Channel in Netapp Ontap Jul 22, 2026
- Medium CVE-2026-14355 ext/openssl: Memory corruption in openssl_encrypt with AES-WRAP-PAD Jul 3, 2026
- Medium CVE-2026-56968 Use of Uninitialized Resource in Gnu Sasl Jun 23, 2026
- Medium CVE-2026-54231 Abrt: unsanitized systemd journal content written to dump directory files enables content injection Jun 13, 2026
- High CVE-2026-54230 Abrt: event handler scripts follow symlinks when writing output files, allowing arbitrary file overwrites Jun 13, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2023-27535 is "An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse...", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 1.61% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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