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Debian LinuxOperating system · Debian

CVE-2021-41990

HIGH · 7.5 CVSS v3.1 Published 2021-10-18
Fix available
A fix is available. Upgrade to 5.9.4 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The gmp plugin in strongSwan before 5.9.4 has a remote integer overflow via a crafted certificate with an RSASSA-PSS signature. For example, this can be triggered by an unrelated self-signed CA certificate sent by an initiator. Remote code execution cannot occur.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The gmp plugin in strongSwan before 5.9.4 contains a remote integer overflow vulnerability in its certificate processing logic when handling RSASSA-PSS signatures. An attacker can trigger this by sending a crafted, unrelated self-signed CA certificate during the authentication phase, potentially causing a denial-of-service condition through the overflow.

MitigationUpgrade strongSwan to version 5.9.4 or later to obtain the patched gmp plugin. If upgrading is not immediately feasible, consider disabling the gmp plugin or restricting remote access to trusted VPN peers only.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Debian LinuxOperating system
Affected:= 10.0= 11.0
FedoraOperating system
Affected:= 33= 34= 35
StrongswanApplication
Affected:>= 5.6.1, < 5.9.4
6gk6108 4am00 2ba2 FirmwareOperating system
Affected:all versions
6gk6108 4am00 2da2 FirmwareOperating system
Affected:all versions
6gk5804 0ap00 2aa2 FirmwareOperating system
Affected:all versions
6gk5812 1aa00 2aa2 FirmwareOperating system
Affected:all versions
6gk5812 1ba00 2aa2 FirmwareOperating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if strongSwan is installed
    Run 'strongswan --version' or check for the presence of strongSwan binaries in /usr/sbin (e.g., 'ls -la /usr/sbin/charon' or 'which ipsec')
    Affected if strongSwan is installed and the version is between 5.6.1 and 5.9.3 inclusive
  2. Identify the installed strongSwan version
    Run 'strongswan --version' and parse the version number, or check package manager (dpkg -l | grep strongswan on Debian, rpm -qa | grep strongswan on Fedora)
    Affected if Version is 5.9.3 or earlier (versions 5.6.1 through 5.9.3 are vulnerable)
  3. Verify if the gmp plugin is enabled
    Check the strongSwan configuration: look for 'gmp' in /etc/strongswan.conf or in the loaded plugins list. Run 'ipsec listplugins' if available, or check /etc/strongswan.d/ for the gmp plugin configuration directory
    Affected if The gmp plugin is loaded or enabled in the configuration
  4. Confirm RSA/PSS signature usage in IPsec configuration
    Review /etc/ipsec.conf and any included configuration files in /etc/ipsec.d/ for 'rsasig' or 'sha2' related policies that may indicate RSASSA-PSS signature handling is configured
    Affected if The VPN is configured to use RSA authentication with RSASSA-PSS signature algorithms, which triggers the vulnerable code path
  5. Check if remote access VPN is exposed
    Review firewall rules and ipsec.conf for 'leftsubnet', 'rightsubnet', and 'remote' settings to determine if the IPsec gateway accepts remote connections from untrusted peers
    Affected if The strongSwan VPN gateway accepts remote connections from untrusted or public networks, allowing an attacker to send the crafted certificate during the authentication phase

You are affected if strongSwan version 5.6.1 through 5.9.3 is installed with the gmp plugin enabled, and the VPN accepts remote connections that could trigger the RSASSA-PSS certificate processing vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.9.4 or later
Fixed in 5.9.4
Interim mitigation

Upgrade strongSwan to version 5.9.4 or later to obtain the patched gmp plugin. If upgrading is not immediately feasible, consider disabling the gmp plugin or restricting remote access to trusted VPN peers only.

Recommended fix High confidence

strongSwan 5.9.4 or later

  1. 1. Identify the current strongSwan version installed (e.g., run 'strongswan -v' or check package manager)
  2. 2. For Debian systems: run 'apt update' followed by 'apt install strongswan' to upgrade to the fixed version
  3. 3. For Fedora systems: run 'dnf update strongswan' to upgrade to the fixed version
  4. 4. For Siemens industrial products: obtain and apply the latest firmware update from Siemens cert-portal
  5. 5. After upgrading, restart the strongSwan service (e.g., 'systemctl restart strongswan' or 'service strongswan restart')
  6. 6. Verify the upgrade was successful by checking the version is 5.9.4 or later
Caveat Ensure any custom strongSwan configurations are compatible with the new version before deploying to production

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-41990 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data