CVE-2022-24903

Rsyslog is a rocket-fast system for log processing. Modules for TCP syslog
reception have a potential heap buffer overflow when octet-counted framing
is used. This can result in a segfault or some other malfunction. As of our
understanding, this vulnerability can not be used for remote code
execution. But there may still be a slight chance for experts to do that.
The bug occurs when the octet count is read. While there is a check for the
maximum number of octets, digits are written to a heap buffer even when the
octet count is over the maximum, This can be used to overrun the memory
buffer. However, once the sequence of digits stop, no additional characters
can be added to the buffer. In our opinion, this makes remote exploits
impossible or at least highly complex. Octet-counted framing is one of two
potential framing modes. It is relatively uncommon, but enabled by default
on receivers. Modules imtcp, imptcp, imgssapi, and imhttp are used
for regular syslog message reception. It is best practice not to directly
expose them to the public. When this practice is followed, the risk is
considerably lower. Module imdiag is a diagnostics module primarily
intended for testbench runs. We do not expect it to be present on any
production installation. Octet-counted framing is not very common. Usually,
it needs to be specifically enabled at senders. If users do not need it,
they can turn it off for the most important modules. This will mitigate the
vulnerability.