From: Matt Caswell Date: Wed, 11 Mar 2026 15:06:32 +0000 (+0000) Subject: Fix a one byte buffer overflow in s_client X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=440ac348bf7ad86aaed3eb6a18c7ce587dccb350;p=thirdparty%2Fopenssl.git Fix a one byte buffer overflow in s_client The buffer used to process user commands when using advanced mode ("-adv") can overflow the buffer by one byte if the the read buffer is exactly BUFSIZZ bytes in length (16k). When processing the buffer we add a NUL terminator to the buffer, so if the buffer is already full then we overwrite by one byte when we add the NUL terminator. This does not represent a security issue because this is entirely local and would be "self-inflicted", i.e. not under attacker control. This issue was reported to use by Igor Morgenstern from AISLE. Reviewed-by: Paul Dale Reviewed-by: Tim Hudson Reviewed-by: Tomas Mraz MergeDate: Thu Mar 12 17:56:37 2026 (Merged from https://github.com/openssl/openssl/pull/30376) --- diff --git a/apps/s_client.c b/apps/s_client.c index ad4980add0e..b48b296966d 100644 --- a/apps/s_client.c +++ b/apps/s_client.c @@ -4199,7 +4199,11 @@ static void user_data_init(struct user_data_st *user_data, SSL *con, char *buf, static int user_data_add(struct user_data_st *user_data, size_t i) { - if (user_data->buflen != 0 || i > user_data->bufmax) + /* + * We must allow one byte for a NUL terminator so i must be less than + * bufmax + */ + if (user_data->buflen != 0 || i >= user_data->bufmax) return 0; user_data->buflen = i;