Debian Security Advisory

DLA-2788-1 strongswan -- LTS security update

Date Reported:
19 Oct 2021
Affected Packages:
Security database references:
In Mitre's CVE dictionary: CVE-2021-41991.
More information:

Researchers at the United States of America National Security Agency (NSA) identified a denial of services vulnerability in strongSwan, an IKE/IPsec suite.

Once the in-memory certificate cache is full it tries to randomly replace lesser used entries. Depending on the generated random value, this could lead to an integer overflow that results in a double-dereference and a call using out-of-bounds memory that most likely leads to a segmentation fault.

Remote code execution can't be ruled out completely, but attackers have no control over the dereferenced memory, so it seems unlikely at this point.

For Debian 9 stretch, this problem has been fixed in version 5.5.1-4+deb9u5.

We recommend that you upgrade your strongswan packages.

For the detailed security status of strongswan please refer to its security tracker page at:

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: