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

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

diff --git a/src/src/tls.c b/src/src/tls.c
index ddee95de2136962cd238407a2dddcf600198434b..e073eadbeb3f47a4c12ed72ce1246324a6589888 100644 (file)
--- a/src/src/tls.c
+++ b/src/src/tls.c
@@ -457,6 +457,9 @@ Returns:       the character
 int
 tls_ungetc(int ch)
 {
+if (ssl_xfer_buffer_lwm <= 0)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
+
 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
 return ch;
 }