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CVE-2023-27538VulnerabilityPublished Updated

CVE-2023-27538: https://github.com/curl/curl · Authentication Bypass by Primary Weakness

Affects https://github.com/curl/curlSource CVE Database V5

0

Not known to be exploited · CVSS 7.7 High : upgrade to 8.0.0 soon.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score
7.7High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
1.4% chance of exploitation in 30 days – higher than 73% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 8.0.0
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 30 Mar 2023

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

What to do

Upgrade curl/curl to 8.0.0.

Affected software

ProductAffectedFixed in
GitHubcurl/curlpkg:github/curl/curlOther threatsAffected
  • <8.0.0
Fixed in
  • 8.0.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should prioritize upgrading libcurl to version 8.0.0 or later where the vulnerability is fixed. For environments where immediate upgrade is not feasible, organizations should audit and restrict local user access to systems running vulnerable libcurl versions to minimize exploitation risk. Additionally, organizations should review and harden SSH configurations to reduce reliance on connection reuse or disable connection pooling features if possible. Monitoring and logging SSH connection reuse events can help detect anomalous reuse patterns indicative of exploitation attempts. Incorporating application-level authentication and authorization checks beyond SSH can provide defense in depth. Security teams should also verify that third-party software and internal tools using libcurl are updated or patched accordingly. Finally, conducting penetration testing and vulnerability scanning focused on libcurl usage can identify vulnerable instances and confirm mitigation effectiveness.

Description

An authentication bypass vulnerability exists in libcurl prior to v8.0.0 where it reuses a previously established SSH connection despite the fact that an SSH option was modified, which should have prevented reuse.libcurl maintains a pool of previously used connections to reuse them for subsequent transfers if the configurations match. However, two SSH settings were omitted from the configuration check, allowing them to match easily, potentially leading to the reuse of an inappropriate connection.

References

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