From 129ab919a8c3abfc17bea776f0774e0ccf33ca09 Mon Sep 17 00:00:00 2001 From: Tobias Brunner Date: Tue, 25 Sep 2018 14:50:08 +0200 Subject: [PATCH] gmp: Fix buffer overflow with very small RSA keys Because `keylen` is unsigned the subtraction results in an integer underflow if the key length is < 11 bytes. This is only a problem when verifying signatures with a public key (for private keys the plugin enforces a minimum modulus length) and to do so we usually only use trusted keys. However, the x509 plugin actually calls issued_by() on a parsed certificate to check if it is self-signed, which is the reason this issue was found by OSS-Fuzz in the first place. So, unfortunately, this can be triggered by sending an invalid client cert to a peer. Fixes: 5955db5b124a ("gmp: Don't parse PKCS1 v1.5 RSA signatures to verify them") Fixes: CVE-2018-17540 --- src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c b/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c index e9a83fdf49a1..a255a40abce2 100644 --- a/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c +++ b/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c @@ -301,7 +301,7 @@ bool gmp_emsa_pkcs1_signature_data(hash_algorithm_t hash_algorithm, data = digestInfo; } - if (data.len > keylen - 11) + if (keylen < 11 || data.len > keylen - 11) { chunk_free(&digestInfo); DBG1(DBG_LIB, "signature value of %zu bytes is too long for key of " -- 2.7.4