Description
When libcurl uses libssh2 with a hashed `known_hosts` file, an unrelated
initial entry can cause host key validation to report a key *mismatch* as a
*missing* key to the `CURLOPT_SSH_KEYFUNCTION` callback.
Published: 2026-10-20
Score: 3.7 Low
EPSS: < 1% Very Low
KEV: No
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Remediation

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Tracking

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8927-1 curl vulnerabilities
Ubuntu USN Ubuntu USN USN-8927-2 curl vulnerabilities
History

Tue, 20 Oct 2026 20:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When libcurl is built with the libssh2 backend and uses a hashed known-hosts file, host key verification can mistakenly report a key mismatch as a missing key to custom verification callbacks. A remote attacker who intercepts or controls the Secure Shell (SSH) connection can exploit this flaw to make a previously pinned server appear as a new host. As a result, the application may inadvertently authenticate to an untrusted server, leading to credential exposure and the receipt of malicious data. When libcurl uses libssh2 with a hashed `known_hosts` file, an unrelated initial entry can cause host key validation to report a key *mismatch* as a *missing* key to the `CURLOPT_SSH_KEYFUNCTION` callback.
Title curl: curl: knownhost callback mismatches key as missing knownhost callback mismatches key as missing
References

Sun, 18 Oct 2026 15:00:00 +0000

Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl

Sat, 17 Oct 2026 00:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When libcurl is built with the libssh2 backend and uses a hashed known-hosts file, host key verification can mistakenly report a key mismatch as a missing key to custom verification callbacks. A remote attacker who intercepts or controls the Secure Shell (SSH) connection can exploit this flaw to make a previously pinned server appear as a new host. As a result, the application may inadvertently authenticate to an untrusted server, leading to credential exposure and the receipt of malicious data.
Title curl: curl: knownhost callback mismatches key as missing
Weaknesses CWE-295
References
Metrics threat_severity

None

 cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'}

threat_severity

Low

Subscriptions

Curl Curl
cve-icon MITRE

Status: PUBLISHED

Assigner: curl

Published:

Updated: 2026-10-20T20:15:13.165Z

Reserved: 2026-09-09T13:17:41.347Z

Link: CVE-2026-87865

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-20T21:17:20.693

Modified: 2026-10-22T16:57:53.407

Link: CVE-2026-87865

cve-icon Redhat

Severity : Low

Publid Date: 2026-10-14T12:00:00Z

Links: CVE-2026-87865 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-20T23:00:23Z

Weaknesses