CVE-2020-28024: Heap buffer underflow in smtp_ungetc()

[exim.git] / src / src / smtp_in.c

diff --git a/src/src/smtp_in.c b/src/src/smtp_in.c
index a8b92d0bed001fadfa0d8acd30987a9bdd35effd..258ec03e4d03e78890e8a5aa2cd85a5e2adf31f7 100644 (file)
--- a/src/src/smtp_in.c
+++ b/src/src/smtp_in.c
@@ -831,6 +831,9 @@ Returns:       the character
 int
 smtp_ungetc(int ch)
 {
+if (smtp_inptr <= smtp_inbuffer)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in smtp_ungetc");
+
 *--smtp_inptr = ch;
 return ch;
 }