CVE-2026-66033 @ Helios

"CVE-2026-66033"
"libssh2-1-1.9.0-2+deb11u1"
"libssh2-1"
"Am I vulnerable?"

Status

accepted_risk

Priority

1.12

Match score

4.0

Risk

InfoLeak MemCorrupt DoS

CVSS

7.5 HIGH

Reason

cpe: libssh2; pkgs: libssh2-1; version: in-range: libssh2-1-1.9.0-2+deb11u1; debian:bullseye libssh2 open; risk:info_disclosure

Created

2026-08-03T02:34:45Z

Updated

2026-08-14T10:17:23Z

Closed

2026-08-03T02:45:15Z

Package interrogation (copy)

Run on the host — click to copy a command. Debian/apt

Package	Commands
libssh2-1-1.9.0-2+deb11u1
libssh2-1

Inventory lookup

Search package inventory across systems, then return here. Create a ticket on systems the matcher missed.

Suggestions: libssh2 · libssh2-1

Same product CVEs in your queue

Other tickets that look like the same product (from match reason). Relate them here to triage this CVE as the primary.

CVE	CVSS	Systems	Status	Matched	Already related
CVE-2026-66032	8.8	Helios, morris, mufasa	accepted_risk	libssh2	—
CVE-2026-66034	7.5	Helios, morris, mufasa	accepted_risk, not_applicable	libssh2	→ CVE-2026-66033	linked here
CVE-2026-66035	7.5	morris, mufasa	not_applicable	libssh2	→ CVE-2026-66033	linked here

Related CVE (same fix)

Point this ticket’s CVE at a higher-priority / same-fix primary so you only triage one.

Other CVEs related to this one as primary:

Related CVE	Note	Tickets
CVE-2026-66034	same product as CVE-2026-66033	morris, mufasa, Helios
CVE-2026-66035	same product as CVE-2026-66033	morris, mufasa

Host OS / kernel

Debian GNU/Linux 11 (bullseye) (11) · debian

Arch

aarch64

kernel_release

uname -r → 6.1.21-v8+

kernel_version

uname -v → #1642 SMP PREEMPT Mon Apr 3 17:24:16 BST 2023

For Linux kernel CVEs, kernel_version (Debian packaging / build string) often decides fixed vs not; kernel_release is used for upstream NVD range compares.

Same CVE on other hosts

Open the ticket for this CVE on another system.

System	Status	Priority	Updated
morris	accepted_risk	7.5	2026-08-22T10:16:55Z	Open
mufasa	accepted_risk	7.5	2026-08-22T10:16:55Z	Open

Description

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

Determination

This is a client-side Denial of Service. 
Any application that uses this libssh2 library to connect to an untrusted SSH server can be crashed by that server.

Update status

Add note only

Mitigation log

2026-08-03T02:39:18Z — affects

This is a client-side Denial of Service. Any application that uses this libssh2 library to connect to an untrusted SSH server can be crashed by that server.

2026-08-03T02:40:44Z

No real danger since we dont ssh to untrusted servers.

References

NVD: CVE-2026-66033