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