dnsmasq: fix CVE-2026-4892

A heap-based out-of-bounds write vulnerability in the DHCPv6
implementation of dnsmasq allows local attackers to execute
arbitrary code with root privileges via a crafted DHCPv6 packet.

Reference:
[ https://nvd.nist.gov/vuln/detail/CVE-2026-4892 ]

Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>
(cherry picked from commit 21c3d7eb6f94f967b5e02fc61cc027d3893764a0)
Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>

2 files changed, 37 insertions, 0 deletions

diff --git a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
index 0de434036a..4060941ad2 100644
--- a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
+++ b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
@@ -16,6 +16,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
            file://dnsmasq-noresolvconf.service \
            file://dnsmasq-resolved.conf \
            file://CVE-2026-4891.patch \
+           file://CVE-2026-4892.patch \
 "
 SRC_URI[sha256sum] = "fd908e79ff37f73234afcb6d3363f78353e768703d92abd8e3220ade6819b1e1"
 
diff --git a/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4892.patch b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4892.patch
new file mode 100644
index 0000000000..01637601a3
--- /dev/null
+++ b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4892.patch
@@ -0,0 +1,36 @@
+commit 011a36c51438c986535a7248ed2e7f424f8e1078
+Author: Simon Kelley <simon@thekelleys.org.uk>
+Date:   Wed Mar 25 23:16:35 2026 +0000
+
+Fix buffer overflow in helper.c with large CLIDs. CVE-2026-4892
+    
+Bug reported bt Royce M <royce@xchglabs.com>
+    
+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: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
+
+diff --git a/src/helper.c b/src/helper.c
+index 72f81fe..2c12801 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, RW_READ))
+        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)