diff -Nru strongswan-5.3.5/debian/changelog strongswan-5.3.5/debian/changelog
--- strongswan-5.3.5/debian/changelog	2018-09-18 11:40:08.000000000 +0000
+++ strongswan-5.3.5/debian/changelog	2018-09-26 18:38:03.000000000 +0000
@@ -1,3 +1,13 @@
+strongswan (5.3.5-1ubuntu3.8) xenial-security; urgency=medium
+
+  * SECURITY UPDATE: Insufficient input validation in gmp plugin
+    - debian/patches/strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch: fix
+      buffer overflow with very small RSA keys in
+      src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c.
+    - CVE-2018-17540
+
+ -- Marc Deslauriers <marc.deslauriers@ubuntu.com>  Wed, 26 Sep 2018 14:38:03 -0400
+
 strongswan (5.3.5-1ubuntu3.7) xenial-security; urgency=medium
 
   * SECURITY UPDATE: Insufficient input validation in gmp plugin
diff -Nru strongswan-5.3.5/debian/patches/series strongswan-5.3.5/debian/patches/series
--- strongswan-5.3.5/debian/patches/series	2018-09-18 11:38:56.000000000 +0000
+++ strongswan-5.3.5/debian/patches/series	2018-09-26 18:37:57.000000000 +0000
@@ -11,3 +11,4 @@
 strongswan-5.3.1-5.6.0_gmp-pkcs1-verify.patch
 strongswan-5.0.1-5.4.0_skeyseed_init.patch
 strongswan-5.1.2-5.6.2_stroke_msg_len.patch
+strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch
diff -Nru strongswan-5.3.5/debian/patches/strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch strongswan-5.3.5/debian/patches/strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch
--- strongswan-5.3.5/debian/patches/strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch	1970-01-01 00:00:00.000000000 +0000
+++ strongswan-5.3.5/debian/patches/strongswan-4.4.0-5.7.0_gmp-pkcs1-overflow.patch	2018-09-26 18:38:00.000000000 +0000
@@ -0,0 +1,35 @@
+From 129ab919a8c3abfc17bea776f0774e0ccf33ca09 Mon Sep 17 00:00:00 2001
+From: Tobias Brunner <tobias@strongswan.org>
+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(-)
+
+Index: strongswan-5.3.5/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c
+===================================================================
+--- strongswan-5.3.5.orig/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c	2018-09-26 14:37:58.780418655 -0400
++++ strongswan-5.3.5/src/libstrongswan/plugins/gmp/gmp_rsa_private_key.c	2018-09-26 14:37:58.780418655 -0400
+@@ -299,7 +299,7 @@ bool gmp_emsa_pkcs1_signature_data(hash_
+ 		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 "