Threat Intelligence / CVE / CVE-2026-55200

CVE-2026-55200 — libssh2

CVSS v3.1 8.1 (HIGH) · CVSS v4.0 9.2 · EPSS 0.5% (higher than 41.4% of all scored CVEs) · Priority 7.7/10 · Published 2026-06-17

As of 2026-06-18, CVE-2026-55200 is a HIGH-severity vulnerability in libssh2, CVSS v3.1 8.1, EPSS 0.5% (41.4th percentile). Threadlinqs Intelligence links 3 tracked threat campaigns to CVE-2026-55200, most recently “Public PoC Released for Critical libssh2 Client-Side SSH Flaw (CVE-2026-55200)”.

Last updated: 2026-06-18

What is CVE-2026-55200?

libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds write vulnerability in ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote code execution.

The record classifies CVE-2026-55200 under weakness class CWE-680. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 97 days ago.

Severity and exploitation probability

CVSS v3.1 base score: 8.1 — HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0 base score: 9.2
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
EPSS (FIRST): 0.5% probability of exploitation in the next 30 days, higher than 41.4% of all scored CVEs
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 7.7/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2026-06-17, last modified 2026-06-18

Is CVE-2026-55200 being exploited?

Weaponised exploit code for CVE-2026-55200 is publicly available. 1 public proof-of-concept repository is tracked for this identifier.

0xBlackash/CVE-2026-55200 (github)

Affected products and versions

libssh2: libssh2

How to fix CVE-2026-55200

No vendor patch reference has been recorded for CVE-2026-55200 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

Threat activity tracking CVE-2026-55200

3 tracked threats in the Threadlinqs corpus reference CVE-2026-55200, either in the campaign’s CVE list or as an indicator on the campaign record.

Public PoC Released for Critical libssh2 Client-Side SSH Flaw (CVE-2026-55200) — CRITICAL · 2026-07-11
Threat Actors Mass-Probe Gitea Docker Deployments for CVE-2026-20896 Authentication Bypass Amid Exploitarium Zero-Day Leak Wave — CRITICAL · 2026-07-06
CVE-2026-55200: libssh2 Integer Overflow to Heap Out-of-Bounds Write in ssh2_transport_read() — CRITICAL · 2026-06-24

Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-06-24. This product uses the NVD API but is not endorsed or certified by the NVD.

Full detection coverage & IOCs for threats exploiting CVE-2026-55200 are available via the Threadlinqs MCP server (Purple tier). View plans →

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