Microsoft SymCrypt, a core cryptographic library in Windows, contains a heap-based buffer overflow in the SymCryptXmssSign function in versions 103.5.0 through 103.10.x. The vulnerability occurs because a 64-bit leaf count value is truncated to 32 bits when passed to a helper function, resulting in a buffer allocation that is too small for XMSS^MT signature computations with tree heights of 32 or greater. This buffer overflow can lead to memory corruption during signature generation. Exploitation requires the use of attacker-controlled parameter sets for XMSS^MT signing, which is unlikely in typical scenarios because signing operations require trusted private keys and are generally performed within HSMs. The vulnerability was addressed and fixed in version 103.11.0 of SymCrypt.

The vulnerability can cause a heap buffer overflow during XMSS^MT signature computation, potentially leading to memory corruption and denial of service or other impacts on integrity. However, exploitation is constrained by the requirement that an application must perform XMSS^MT signing with attacker-controlled parameters, which is uncommon. Additionally, XMSS(^MT) signing is intended only for testing and should be performed in HSMs, limiting practical exposure. There are no known exploits in the wild.

A fix for this vulnerability is available in SymCrypt version 103.11.0. Users and developers should upgrade to this version to remediate the issue. Since this vulnerability affects a specific and uncommon use case (XMSS^MT signing with attacker-controlled parameters), and signing should be performed in HSMs, typical users may not be exposed. No additional mitigations are indicated by the vendor advisory.