From 2f029069825270a3b91eb5f50bb8477ed7f761d3 Mon Sep 17 00:00:00 2001 From: Simon Kelley Date: Wed, 25 Mar 2026 23:16:35 +0000 Subject: [PATCH] Fix buffer overflow in helper.c with large CLIDs. CVE-2026-4892 Bug reported bt Royce M Location: helper.c:265-270 DHCPv6 CLIDs can be up to 65535 bytes. When --dhcp-script is configured, the helper hex-encodes raw CLID bytes via sprintf("%.2x") into daemon->packet (5131 bytes). A 1000-byte CLID writes ~3000 bytes. The helper process retains root privileges. Note: log6_packet() correctly caps CLID to 100 bytes for logging, but the helper code path was missed. CVE: CVE-2026-4892 Upstream-Status: Backport [https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=10e6b5b83e80749cba7b090d7780b29f908f0571] Signed-off-by: Hugo SIMELIERE (Schneider Electric) --- src/helper.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/helper.c b/src/helper.c index b9da2259..3a31e618 100644 --- a/src/helper.c +++ b/src/helper.c @@ -261,8 +261,8 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd) data.hostname_len + data.ed_len + data.clid_len, 1)) continue; - /* CLID into packet */ - for (p = daemon->packet, i = 0; i < data.clid_len; i++) + /* CLID into packet: limit to 100 bytes to avoid overflowing buffer. */ + for (p = daemon->packet, i = 0; i < data.clid_len && i < 100; i++) { p += sprintf(p, "%.2x", buf[i]); if (i != data.clid_len - 1) -- 2.43.0