CVE-2026-55199
Pre-auth DoS in libssh2 via SSH MSG_EXT_INFO; crafted ext count loops CPU.
Is CVE-2026-55199 being exploited?
Not confirmed. CVE-2026-55199 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 0.92% probability of exploitation in the next 30 days.
How severe is CVE-2026-55199?
CVE-2026-55199 is rated High with a CVSS score of 8.2. 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-2026-55199?
Yes. A fix has been recorded for CVE-2026-55199. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-55199 affect?
CVE-2026-55199 affects libssh2 <= 1.11.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-55199?
Upgrade libssh2 to >= 1.11.1; verify dependent apps.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Pre-auth DoS: attacker-server ext count 0xFFFFFFFF causes client CPU loop during KEX, leading to DoS.
Immediate action required
- 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.