In verify_emsa_pkcs1_signature() in gmp_rsa_public_key.c in the gmp plugin in strongSwan 4.x and 5.x before 5.7.0, the RSA implementation based on GMP does not reject excess data after the encoded algorithm OID during PKCS#1 v1.5 signature verification. Similar to the flaw in the same version of strongSwan regarding digestAlgorithm.parameters, a remote attacker can forge signatures when small public exponents are being used, which could lead to impersonation when only an RSA signature is used for IKEv2 authentication.
http://lists.opensuse.org/opensuse-security-announce/2019-11/msg00077.html
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00001.html
https://lists.debian.org/debian-lts-announce/2018/09/msg00032.html
https://security.gentoo.org/glsa/201811-16
https://usn.ubuntu.com/3771-1/
Source: MITRE
Published: 2018-09-26
Updated: 2019-12-01
Type: CWE-347
Base Score: 5
Vector: AV:N/AC:L/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 7.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Impact Score: 3.6
Exploitability Score: 3.9
Severity: HIGH