From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Thu, 21 Mar 2019 20:01:03 +0000 (+0000)
Subject: Harden plaintext authenticator
X-Git-Url: https://git.exim.org/exim.git/commitdiff_plain/e5b942ae007d0533fbd599c64d550f3a8355b940?hp=332ebeaf8139b2b75f475880fc14b63c7c45c706

Harden plaintext authenticator

Cherry-picked from: f9fc942757
---

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 3d63725f2..c34e60d1c 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -34,6 +34,11 @@ JH/10 OpenSSL: Fix aggregation of messages.  Previously, when PIPELINING was
       dropped connections and sometimes bounces generated by a peer sending
       to this system.
 
+JH/11 Harden plaintext authenticator against a badly misconfigured client-send
+      string.  Previously it was possible to cause undefined behaviour in a
+      library routine (usually a crash).  Found by "zerons".
+
+
 
 Exim version 4.92
 -----------------
diff --git a/src/src/auths/plaintext.c b/src/src/auths/plaintext.c
index 7a0f78852..fa05b0ad5 100644
--- a/src/src/auths/plaintext.c
+++ b/src/src/auths/plaintext.c
@@ -223,11 +223,7 @@ while ((s = string_nextinlist(&text, &sep, big_buffer, big_buffer_size)))
       if (ss[i+1] != '^')
 	ss[i] = 0;
       else
-        {
-        i++;
-        len--;
-        memmove(ss + i, ss + i + 1, len - i);
-        }
+        if (--len > ++i) memmove(ss + i, ss + i + 1, len - i);
 
   /* The first string is attached to the AUTH command; others are sent
   unembellished. */