CVE-2026-55200Network attack vectorHinoki check available

Code execution via unchecked SSH packet length

Published Jun 17, 2026 · Updated Jul 14, 2026

Heap corruption in libssh2 1.11.1 and earlier allows remote attackers to execute code via crafted SSH transport packets. In src/transport.c, ssh2_transport_read() accepts an oversized packet_length before adding framing and authentication lengths, allowing integer wraparound to underallocate the heap buffer. The affected path requires an encrypted SSH session using a cipher that requires full-packet processing; execution occurs in the consuming client application's context.

CVSS severity9.2
Critical
EPSS probability4.02%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Heap corruption in libssh2 1.11.1 and earlier allows remote attackers to execute code via crafted SSH transport packets. In src/transport.c, ssh2_transport_read() accepts an oversized packet_length before adding framing and authentication lengths, allowing integer wraparound to underallocate the heap buffer. The affected path requires an encrypted SSH session using a cipher that requires full-packet processing; execution occurs in the consuming client application's context.

The record

CVE
CVE-2026-55200
Published
Jun 17, 2026
Updated
Jul 14, 2026
Vendor
The libssh2 Project
Product
libssh2
Classifications
CWE-680, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=1.11.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The libssh2 Project · libssh2version=0 <=1.11.1

Published CVSS scores

8.1Amazon LinuxCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
9.2VulnCheckCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
8.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
8.1VulnCheckCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-680Integer Overflow to Buffer Overflow
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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