dnsmasq: fix CVE-2026-4893

An information disclosure vulnerability in dnsmasq allows remote
attackers to bypass source checks via a crafted DNS packet with
RFC 7871 client subnet information.

Reference:
[ https://nvd.nist.gov/vuln/detail/CVE-2026-4893 ]

Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

2 files changed, 35 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 cf900328ed..4ae650f7e7 100644
--- a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
+++ b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
@@ -19,6 +19,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
            file://CVE-2026-4890.patch \
            file://CVE-2026-4891.patch \
            file://CVE-2026-4892.patch \
+           file://CVE-2026-4893.patch \
 "
 SRC_URI[sha256sum] = "fd908e79ff37f73234afcb6d3363f78353e768703d92abd8e3220ade6819b1e1"
 
diff --git a/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch
new file mode 100644
index 0000000000..af7e4119e1
--- /dev/null
+++ b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch
@@ -0,0 +1,34 @@
+commit 434d68f2eb1a58744470698483a3ae09b5a9a870
+Author: Simon Kelley <simon@thekelleys.org.uk>
+Date:   Wed Mar 25 23:22:37 2026 +0000
+
+Fix broken client subnet validation. CVE-2026-4893
+    
+Bug report from Royce M <royce@xchglabs.com>
+    
+Location: forward.c:713, edns0.c:421
+    
+With --add-subnet enabled, process_reply() passes the OPT record
+length (~23 bytes) instead of the packet length to check_source().
+All internal bounds checks fail, and the function always returns 1.
+ECS source validation per RFC 7871 Section 9.2 is completely bypassed.
+
+CVE: CVE-2026-4893
+
+Upstream-Status: Backport [ https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=e3a26d092e47bf1d18aeadb758e4ca35c83b5f2d ]
+
+Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
+
+diff --git a/src/forward.c b/src/forward.c
+index e2f64c0..208480d 100644
+--- a/src/forward.c
++++ b/src/forward.c
+@@ -724,7 +724,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
+       /* Get extended RCODE. */
+       rcode |= sizep[2] << 4;
+       
+-      if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, plen, pheader, query_source))
++      if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, n, pheader, query_source))
+        {
+          my_syslog(LOG_WARNING, _("discarding DNS reply: subnet option mismatch"));
+          return 0;