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NVD / CVE Program· CNA VulnCheck

CVE-2026-55200: libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c

Noroxi assessment

Priority: Monitor (action score 37/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 3.8% (FIRST EPSS); higher than 90.2% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: libssh2 libssh2 97acf3dfda80c91c3a8c9f2372546301d4a1a7a8; azl3 libssh2 1.11.1-2 on Azure Linux 3.0 1.11.1-3; azl3 libssh2 1.11.1-3 on Azure Linux 3.0 1.11.1-3.

Low priority for now. Upgrade to libssh2 libssh2 97acf3dfda80c91c3a8c9f2372546301d4a1a7a8; azl3 libssh2 1.11.1-2 on Azure Linux 3.0 1.11.1-3; azl3 libssh2 1.11.1-3 on Azure Linux 3.0 1.11.1-3 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

libssh2 1.11.1, fixed in commit 97acf3d, 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.

CriticalCVSS 9.2 · v4.0—Proof of concept Fix available
Published
Jun 17, 2026
Updated
Oct 22, 2026
EPSS
3.8% · 90th percentile

Report tools

JSON

Action score

37

Monitor

Low priority for now.

CVSS
36 / 40 · 9.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 3.8%

CISA SSVC decision

Exploitation
proof of concept
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · VulnCheck
9.2
NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-55200

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
libssh2libssh2

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • libssh2 libssh21.11.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.

  • libssh2 libssh2

    • 1.11.1affected
    • 1c3f1b7da588f2652260285529ec3c1f1125eb4e and later · before 97acf3dfda80c91c3a8c9f2372546301d4a1a7a8affected · git

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.21libssh2before 1.11.1-r21.11.1-r2
Alpine:v3.23libssh2before 1.11.1-r31.11.1-r3
Alpine:v3.24chromium-rustbefore 1.96.1-r01.96.1-r0
Alpine:v3.24rustbefore 1.96.1-r01.96.1-r0
Debian:13libssh2before 1.11.1-1+deb13u11.11.1-1+deb13u1
Debian:14libssh2before 1.11.1-41.11.1-4
openSUSE:Leap 16.0libssh2_orgbefore 1.11.1-160000.4.11.11.1-160000.4.1
openSUSE:Tumbleweedlibssh2_orgbefore 1.11.1-3.11.11.1-3.1
Red Hat:hummingbird:1libssh2before 0:1.11.1-8.hum10:1.11.1-8.hum1
Red Hat:hummingbird:1libssh2-develbefore 0:1.11.1-8.hum10:1.11.1-8.hum1
Red Hat:hummingbird:1libssh2-docsbefore 0:1.11.1-8.hum10:1.11.1-8.hum1
SUSE:Linux Micro 6.2libssh2_orgbefore 1.11.1-160000.4.11.11.1-160000.4.1

Same product

libssh2: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-3861An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SSH packets with a padding length value greater than the packet
    38Monitor
  • CVE-2019-3860An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SFTP packets with empty payloads are parsed.
    38Monitor
  • CVE-2019-3858An out of bounds read flaw was discovered in libssh2 before 1.8.1 when a specially crafted SFTP packet is received from the server.
    38Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-7598May 1, 2026 · libssh2 userauth.c userauth_password integer overflow
    27Monitor
  • ← EarlierCVE-2026-55199Jun 17, 2026 · libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
    32Monitor
  • Later →CVE-2025-15661Jun 18, 2026 · libssh2 - Heap Buffer Over-read via sftp_symlink() in sftp.c
    33Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
libssh2 libssh297acf3dfda80c91c3a8c9f2372546301d4a1a7a8Vendor (CNA)
azl3 libssh2 1.11.1-2 on Azure Linux 3.01.11.1-3 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 libssh2 1.11.1-3 on Azure Linux 3.01.11.1-3 · CBL-Mariner ReleasesMicrosoft (MSRC)
alpine:chromium-rust1.96.1-r0 · Alpine:v3.24Package registry (OSV)
alpine:libssh21.11.1-r2 · Alpine:v3.21Package registry (OSV)
alpine:rust1.96.1-r0 · Alpine:v3.24Package registry (OSV)
debian:libssh21.11.1-1+deb13u1 · Debian:13Package registry (OSV)
opensuse:libssh2_org1.11.1-3.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:libssh20:1.11.1-8.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libssh2-devel0:1.11.1-8.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:libssh2-docs0:1.11.1-8.hum1 · Red Hat:hummingbird:1Package registry (OSV)
suse:libssh2_org1.11.1-160000.4.1 · SUSE:Linux Micro 6.2Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×3

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:102026-06-23
Proof-of-concept repository on GitHubstars:42026-06-29
Proof-of-concept repository on GitHubstars:02026-07-02

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+5 d
  3. TodayNov 7, 2026+143 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-680 · Integer Overflow to Buffer Overflow

CVSS vector

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/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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records