knownhost callback mismatches key as missing
Only libcurl built with the libssh2 backend, using SFTP or SCP with a hashed known_hosts file, is affected in versions 7.69.1 through 8.22.0. curl rates it Low. Fixed in 8.23.0.
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- The rating the maker of the software gives it. Shown when it differs from the CVSS level.What do these mean? →
- Low (curl)
- Fix
- Fixed in 8.14.3, 8.16.2, 8.20.2, 8.23.0
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: poc
- Automatable: no
- Technical impact: total
Summary
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.
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: poc · Automatable: no · Technical impact: total
- Record last updated
Affected versions
- curl curl
From 8.22.0 · through 8.22.0; From 8.21.0 · through 8.21.0; From 8.20.0 · through 8.20.0; From 8.19.0 · through 8.19.0; From 8.18.0 · through 8.18.0; From 8.17.0 · through 8.17.0; From 8.16.0 · through 8.16.0; From 8.15.0 · through 8.15.0; From 8.14.1 · through 8.14.1; From 8.14.0 · through 8.14.0; From 8.13.0 · through 8.13.0; From 8.12.1 · through 8.12.1; From 8.12.0 · through 8.12.0; From 8.11.1 · through 8.11.1; From 8.11.0 · through 8.11.0; From 8.10.1 · through 8.10.1; From 8.10.0 · through 8.10.0; From 8.9.1 · through 8.9.1; From 8.9.0 · through 8.9.0; From 8.8.0 · through 8.8.0; From 8.7.1 · through 8.7.1; From 8.7.0 · through 8.7.0; From 8.6.0 · through 8.6.0; From 8.5.0 · through 8.5.0; From 8.4.0 · through 8.4.0; From 8.3.0 · through 8.3.0; From 8.2.1 · through 8.2.1; From 8.2.0 · through 8.2.0; From 8.1.2 · through 8.1.2; From 8.1.1 · through 8.1.1; From 8.1.0 · through 8.1.0; From 8.0.1 · through 8.0.1; From 8.0.0 · through 8.0.0; From 7.88.1 · through 7.88.1; From 7.88.0 · through 7.88.0; From 7.87.0 · through 7.87.0; From 7.86.0 · through 7.86.0; From 7.85.0 · through 7.85.0; From 7.84.0 · through 7.84.0; From 7.83.1 · through 7.83.1; From 7.83.0 · through 7.83.0; From 7.82.0 · through 7.82.0; From 7.81.0 · through 7.81.0; From 7.80.0 · through 7.80.0; From 7.79.1 · through 7.79.1; From 7.79.0 · through 7.79.0; From 7.78.0 · through 7.78.0; From 7.77.0 · through 7.77.0; From 7.76.1 · through 7.76.1; From 7.76.0 · through 7.76.0; From 7.75.0 · through 7.75.0; From 7.74.0 · through 7.74.0; From 7.73.0 · through 7.73.0; From 7.72.0 · through 7.72.0; From 7.71.1 · through 7.71.1; From 7.71.0 · through 7.71.0; From 7.70.0 · through 7.70.0; From 7.69.1 · through 7.69.1
References 3
hackerone.com
Questions about CVE-2026-87865
What does this mean?
When a host is already pinned in a hashed known_hosts file, a trust-on-first-use known-host callback can fail to match its key and treat the host as new. libcurl then authenticates to the endpoint, which may be hostile if an attacker controls or intercepts the SSH server.Source: curl.se, curl.se
Am I affected, and how do I check?
The affected range is curl 7.69.1 through 8.22.0. To check, run curl --version and look for libssh2 in the feature list, then review whether the transfers use SFTP or SCP, whether known_hosts is hashed, and whether CURLOPT_SSH_KEYFUNCTION is set.Source: curl.se, curl.se
What should I do about it?
Upgrade to curl 8.23.0, or to the backported fixed releases 8.14.3, 8.16.2, or 8.20.2 if you stay on those branches. Until then, avoid the libssh2 backend for SFTP and SCP transfers.Source: curl.se, curl.se
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.Source: cve.now feed data