`CVE-2021-3634` libssh

Affected software	libssh
Severity	6.5 Medium CVSS 3.1 2 scores
Weakness	Out-of-bounds write (CWE-787)
Published	31 Aug 2021
Updated	17 Jun 2026

Description

A flaw has been found in libssh in versions prior to 0.9.6. The SSH protocol keeps track of two shared secrets during the lifetime of the session. One of them is called secret_hash and the other session_id. Initially, both of them are the same, but after key re-exchange, previous session_id is kept and used as an input to new secret_hash. Historically, both of these buffers had shared length variable, which worked as long as these buffers were same. But the key re-exchange operation can also change the key exchange method, which can be based on hash of different size, eventually creating "secret_hash" of different size than the session_id has. This becomes an issue when the session_id memory is zeroed or when it is used again during second key re-exchange.

Exploitation status

No public exploit

No exploit has been reported in the sources we check. Published 5 years ago.

CISA KEV not listed
VulnCheck KEV not listed
CISA Vulnrichment no assessment published
Indexed PoC none indexed
EPSS 4.7% chance in 30 days

Waratek protection

Outside Waratek scope

A Java vulnerability, but not one Waratek protects. It affects only Java on a user's desktop (applets, Web Start, JavaFX, the installer), sits in a product the Waratek agent can't be installed into, or is in a package we don't expect in business applications. The decision below says which.

Protection none
Action not pursued none
Review automated Upstream data
Record active

Decided by	The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached
Finding	This CVE names only products the Waratek agent cannot be installed into (netapp/cloud_backup). They ship as sealed appliance images or as native code with no application JVM, so there is no start-up line to add -javaagent to. The vulnerability may well be a Java one; it is permanently out of ARMR's reach rather than outside its subject.

Decided by

The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

Finding

This CVE names only products the Waratek agent cannot be installed into (netapp/cloud_backup). They ship as sealed appliance images or as native code with no application JVM, so there is no start-up line to add -javaagent to. The vulnerability may well be a Java one; it is permanently out of ARMR's reach rather than outside its subject.

CVSS

6.5 MEDIUM v3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

Version Score Band Vector Assigner Type

CVSS 3.1 6.5 MEDIUM CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H NVD Primary published

CVSS 2.0 4.0 none AV:N/AC:L/Au:S/C:N/I:N/A:P NVD Primary

Version	Score	Band	Vector	Assigner	Type
CVSS 3.1	6.5	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`	NVD	Primary	published
CVSS 2.0	4.0	none	`AV:N/AC:L/Au:S/C:N/I:N/A:P`	NVD	Primary

Affected software and releases

Oracle advisories

Advisory	Type	Quarter	Products Oracle names in its risk matrix
Oracle Critical Patch Update January 2022 ↗	CPU	2022-Q1	Oracle MySQL / Workbench: libssh (8.0.27 and prior)

Advisory

Type

Quarter

Products Oracle names in its risk matrix

Oracle Critical Patch Update January 2022 ↗

CPU

2022-Q1

Oracle MySQL / Workbench: libssh (8.0.27 and prior)

Oracle components and versions

Family	Component	Versions, as Oracle lists them	Read as
Oracle MySQL	Workbench: libssh	8.0.27 and prior

Family

Component

Versions, as Oracle lists them

Read as

Oracle MySQL

Workbench: libssh

8.0.27 and prior

Products and versions

7 products, 10 version entries

Source	Vendor	Product	Scheme	Affected versions
nvd	debian	debian linux	generic	10.0 · 11.0
nvd	fedoraproject	fedora	generic	33 · 34 · 35
nvd	libssh	libssh	generic	≥ 0.9.1 and ＜ 0.9.6
nvd	netapp	cloud backup	generic	any version
nvd	oracle	mysql workbench	generic	≤ 8.0.27
nvd	redhat	enterprise linux	generic	8.0
nvd	redhat	virtualization	generic	4.0

Source

Vendor

Product

Scheme

Affected versions

nvd

debian

debian linux

generic

10.0 · 11.0

nvd

fedoraproject

fedora

generic

33 · 34 · 35

nvd

libssh

generic

≥ 0.9.1 and ＜ 0.9.6

nvd

netapp

cloud backup

generic

any version

nvd

oracle

mysql workbench

generic

≤ 8.0.27

nvd

redhat

enterprise linux

generic

8.0

nvd

redhat

virtualization

generic

4.0

References

URL	Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1978810	Issue Tracking, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/
https://security.gentoo.org/glsa/202312-05
https://security.netapp.com/advisory/ntap-20211004-0003/	Third Party Advisory
https://www.debian.org/security/2021/dsa-4965	Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html	Patch, Third Party Advisory

URL

Timeline

Published	2021-08-31	By the CVE Program.
NVD record modified	2026-06-17	NVD's own last-modified date for this record.

Published

2021-08-31

By the CVE Program.

NVD record modified

2026-06-17

NVD's own last-modified date for this record.

How VRT decided (15 of 24 rules ran)

15 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification no match A researcher's recorded decision for this specific CVE

5 manual classification no match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side no match Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven no match An OSV.dev record of this CVE affecting a package published to Maven Central. When every such package is one business applications do not use (Minecraft mods and launchers, Fastjson) and no tracked product is named by CPE, it settles the CVE as Outside Waratek scope instead

10 cna-maven-package no match An affected Maven artifact named by the CNA itself

11 known-cpe-product no match An NVD CPE naming a product ARMR tracks

12 cna-cpe-product no match A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family no match A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product no match A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product decided it matched Outside Waratek scope Named products cannot host a Java agent: netapp/cloud_backup

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint not reached A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

18 open-source-maven not reached The affected package being open source on Maven, so the fix can be read

19 poc-derivable not reached An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit not reached Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match not reached A vulnerability class already blocked by an ARMR security rule

22 exploited-no-fix-or-poc not reached Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold not reached Medium or Low severity, no CISA or VulnCheck KEV listing, no PoC clearing the evidence bar, no CISA verdict, no Oracle advisory

24 no-exploit-published not reached Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all

Products the scope rules checked

The products this CVE's record names, and whether VRT tracks each one. The scope rules decided on these.

Vendor Product Tracked CPE Source

libssh libssh not tracked cpe:2.3:a:libssh:libssh:*:*:*:*:*:*:*:*

redhat virtualization not tracked cpe:2.3:a:redhat:virtualization:4.0:*:*:*:*:*:*:*

redhat enterprise_linux not tracked cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:-:*:*:*

debian debian_linux not tracked cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

fedoraproject fedora not tracked cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

oracle mysql_workbench not tracked cpe:2.3:a:oracle:mysql_workbench:*:*:*:*:*:*:*:*

netapp cloud_backup not tracked cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*

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