From 2017d88dbc096381d4f348d2fb08bfb3c2b7ed73 Mon Sep 17 00:00:00 2001 From: Katie Hockman Date: Mon, 14 Oct 2019 16:42:21 -0400 Subject: [PATCH] [release-branch.go1.12-security] crypto/dsa: prevent bad public keys from causing panic dsa.Verify might currently use a nil s inverse in a multiplication if the public key contains a non-prime Q, causing a panic. Change this to check that the mod inverse exists before using it. Fixes CVE-2019-17596 Change-Id: I94d5f3cc38f1b5d52d38dcb1d253c71b7fd1cae7 Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/572809 Reviewed-by: Filippo Valsorda (cherry picked from commit 9119dfb0511326d4485b248b83d4fde19c95d0f7) Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/575232 --- src/crypto/dsa/dsa.go | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/crypto/dsa/dsa.go b/src/crypto/dsa/dsa.go index 575314b1b4689..2fc4f1f05bfb0 100644 --- a/src/crypto/dsa/dsa.go +++ b/src/crypto/dsa/dsa.go @@ -279,6 +279,9 @@ func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool { } w := new(big.Int).ModInverse(s, pub.Q) + if w == nil { + return false + } n := pub.Q.BitLen() if n&7 != 0 {