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Debian LTS Advisory DLA-2788-1                [email protected]
https://www.debian.org/lts/security/                    Thorsten Alteholz
October 20, 2021                              https://wiki.debian.org/LTS
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Package        : strongswan
Version        : 5.5.1-4+deb9u5
CVE ID         : CVE-2021-41991

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 

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

For Debian 9 stretch, this problem has been fixed in version 

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: https://wiki.debian.org/LTS