Validate NTLM challenge fields.

[~andy/fetchmail] / ntlmsubr.c

diff --git a/ntlmsubr.c b/ntlmsubr.c
index 9321d26e7c99af92af44c7e677d5dc6f730b8a7c..63cbed8f34a91fae338e3f1c0f6f6044de554895 100644 (file)
--- a/ntlmsubr.c
+++ b/ntlmsubr.c
@@ -55,7 +55,8 @@ int ntlm_helper(int sock, struct query *ctl, const char *proto)
     if ((result = gen_recv(sock, msgbuf, sizeof msgbuf)))
        goto cancelfail;
 
-    if ((result = from64tobits (&challenge, msgbuf, sizeof(challenge))) < 0)
+    if ((result = from64tobits (&challenge, msgbuf, sizeof(challenge))) < 0
+           || result < ((void *)&challenge.context - (void *)&challenge))
     {
        report (stderr, GT_("could not decode BASE64 challenge\n"));
        /* We do not goto cancelfail; the server has already sent the
@@ -64,6 +65,23 @@ int ntlm_helper(int sock, struct query *ctl, const char *proto)
        return PS_AUTHFAIL;
     }
 
+    /* validate challenge:
+     * - ident
+     * - message type
+     * - that offset points into buffer
+     * - that offset + length does not wrap
+     * - that offset + length is not bigger than buffer */
+    if (0 != memcmp("NTLMSSP", challenge.ident, 8)
+           || challenge.msgType != 2
+           || challenge.uDomain.offset > result
+           || challenge.uDomain.offset + challenge.uDomain.len < challenge.uDomain.offset
+           || challenge.uDomain.offset + challenge.uDomain.len > result)
+    {
+       report (stderr, GT_("NTLM challenge contains invalid data.\n"));
+       result = PS_AUTHFAIL;
+       goto cancelfail;
+    }
+
     if (outlevel >= O_DEBUG)
        dumpSmbNtlmAuthChallenge(stdout, &challenge);