dnsmasq: fix CVE-2026-4891

A heap-based out-of-bounds read vulnerability in the
DNSSEC validation of dnsmasq allows remote attackers
to cause a denial of service via a crafted DNS packet.

Reference:
[ https://nvd.nist.gov/vuln/detail/CVE-2026-4891 ]

Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>
(cherry picked from commit a9de48a9fa55a254c0bf2eb528c81bd90e015c03)
Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>

2 files changed, 41 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 59509ecba2..0de434036a 100644
--- a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
+++ b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
@@ -15,6 +15,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
            file://dnsmasq-resolvconf.service \
            file://dnsmasq-noresolvconf.service \
            file://dnsmasq-resolved.conf \
+           file://CVE-2026-4891.patch \
 "
 SRC_URI[sha256sum] = "fd908e79ff37f73234afcb6d3363f78353e768703d92abd8e3220ade6819b1e1"
 
diff --git a/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4891.patch b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4891.patch
new file mode 100644
index 0000000000..e721f5ec0b
--- /dev/null
+++ b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4891.patch
@@ -0,0 +1,40 @@
+commit 2cacea42e4d45717bd0ce3ccfe8e78960245e5da
+Author: Simon Kelley <simon@thekelleys.org.uk>
+Date:   Wed Mar 25 23:04:08 2026 +0000
+
+Verify rdlen field in RRSIG packets. CVE-2026-4891
+    
+Bug report from Royce M <royce@xchglabs.com>
+    
+This avoids crafted packets which give a value for rdlen _less_
+then the space taken up by the fixed data and the signer's name
+and engender a negative calculated length for the signature.
+
+CVE: CVE-2026-4891
+
+Upstream-Status: Backport [ https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=788b4e0f6c05217981b512bed4e5fea6f8855d01 ]
+
+Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
+
+diff --git a/src/dnssec.c b/src/dnssec.c
+index 0860daa..4bb0495 100644
+--- a/src/dnssec.c
++++ b/src/dnssec.c
+@@ -546,10 +546,14 @@ static int validate_rrset(time_t now, struct dns_header *header, size_t plen, in
+ 
+           *ttl_out = ttl;
+         }
+-       
++
++      /* Don't trust rdlen not to be too small and give us a negative sig_len
++        It has already been checked that it doesn't run us off the end
++        of the packet. */
++      if ((sig_len = rdlen - (p - psav)) <= 0)
++       return STAT_BOGUS;
++
+       sig = p;
+-      sig_len = rdlen - (p - psav);
+-              
+       nsigttl = htonl(orig_ttl);
+       
+       hash->update(ctx, 18, psav);