The olmsessiondescribe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow. The Olm session object represents a cryptographic channel between two parties. Therefore, its state is partially controllable by the remote party of the channel. Attackers can construct a crafted sequence of messages to manipulate the state of the receiver's session in such a way that, for some buffer sizes, a buffer overflow happens on a call to olmsessiondescribe. Furthermore, safe buffer sizes were undocumented. The overflow content is partially controllable by the attacker and limited to ASCII spaces and digits. The known affected products are Element Web And SchildiChat Web.

Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olmpkdecrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.

An issue was discovered in Matrix libolm through 3.2.16. The AES implementation is vulnerable to cache-timing attacks due to use of S-boxes. This is related to software that uses a lookup table for the SubWord step. This refers to the libolm implementation of Olm. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.

An issue was discovered in Matrix libolm through 3.2.16. Cache-timing attacks can occur due to use of base64 when decoding group session keys. This refers to the libolm implementation of Olm. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.

An issue was discovered in Matrix libolm through 3.2.16. There is Ed25519 signature malleability due to lack of validation criteria (does not ensure that S < n). This refers to the libolm implementation of Olm. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.