Cyber Resilience

CVE-2026-55200

Libssh2 ≤ 1.11.1

Public PoC
Published
17 June 2026
Modified
14 July 2026
Patch / advisory
View advisory
CVSS Score v4 9.2
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.020 79th percentile
Risk Priority 49 floored blend · peak EPSS

Summary

CVE-2026-55200 is a critical-severity Integer Overflow to Buffer Overflow (CWE-680) vulnerability in Libssh2 Libssh2. Its CVSS base score is 9.2 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 21% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

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…

more

achieve remote code execution.

CWE(s)
CWE-680

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-66035Same product: Libssh2 Libssh2
CVE-2025-15661Same product: Libssh2 Libssh2
CVE-2026-66033Same product: Libssh2 Libssh2
CVE-2026-58050Same product: Libssh2 Libssh2
CVE-2026-7598Same product: Libssh2 Libssh2
CVE-2026-66032Same product: Libssh2 Libssh2
CVE-2026-66034Same product: Libssh2 Libssh2
CVE-2026-58051Same product: Libssh2 Libssh2
CVE-2026-55199Same product: Libssh2 Libssh2
CVE-2025-23326Shared CWE-680

Affected Assets

libssh2
libssh2
≤ 1.11.1

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and analysis (static, dynamic, fuzzing) finds integer-overflow-to-allocation defects before deployment.

SA-15 Development Process, Standards, and Tools partial match

Mandates documented development standards and tools that enforce secure coding rules against unsafe integer arithmetic.

SA-8 Security and Privacy Engineering Principles partial match

Requires engineering principles such as safe arithmetic and bounds-checked allocation that directly stop integer overflow during memory-size computation.

SI-10 Information Input Validation partial match

Validates untrusted size/offset inputs before they reach allocation calculations, structurally blocking the integer overflow path.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prevent integer-overflow flaws during development, but eliminating only this CWE covers only part of the broad control intent.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect integer-overflow-to-buffer-overflow conditions during development.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates practices that can catch integer overflows before deployment.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify safe integer handling and bounds checking.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles encourage use of safe arithmetic libraries and overflow detection.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly require prevention of integer overflows that lead to buffer overflows.

References