CVE-2026-66033
Pre-auth integer underflow in libssh2 lets malicious SSH servers crash clients.
Is CVE-2026-66033 being exploited?
Not confirmed. CVE-2026-66033 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.58% probability of exploitation in the next 30 days.
How severe is CVE-2026-66033?
CVE-2026-66033 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-66033?
Yes. A fix has been recorded for CVE-2026-66033. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-66033 affect?
CVE-2026-66033 affects libssh2 (<= 1.11.1), SFTP/SCP clients using libssh2, Applications using libssh2 (e.g., curl with libssh2 backend), Embedded devices and custom apps linking libssh2. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-66033?
Upgrade libssh2 to the commit a2ed82d / latest release and rebuild dependent apps.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote pre-auth denial-of-service: malicious SSH server can trigger OOB read and massive memcpy to crash libssh2-based clients.
Patch when possible
- affected<= 1.11.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.