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dnsmasq: fix CVE-2026-4890

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A Denial of Service (DoS) vulnerability in the DNSSEC validation of
dnsmasq allows remote attackers to cause a denial of service via a
crafted DNS packet.

This patch is used by debian bookworm (2.90-4_deb12u2).
It is also referenced here [1].

[1] https://thekelleys.org.uk/dnsmasq/CVE/CVE-2026-4890.dnsmasq-2.91.diff

Signed-off-by: Benjamin Robin (Schneider Electric) <benjamin.robin@bootlin.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>
This commit is contained in:
Benjamin Robin (Schneider Electric)
2026-07-21 11:35:45 +02:00
committed by Anuj Mittal
parent 2bc33d99c9
commit 30eaef2541
2 changed files with 76 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files
meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb
+1
View File
@@ -21,6 +21,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
file://CVE-2026-4893.patch \
file://CVE-2026-5172.patch \
file://CVE-2026-2291.patch \
file://CVE-2026-4890.patch \
"
SRC_URI[sha256sum] = "8f6666b542403b5ee7ccce66ea73a4a51cf19dd49392aaccd37231a2c51b303b"
meta-networking/recipes-support/dnsmasq/files/CVE-2026-4890.patch
+75
View File
@@ -0,0 +1,75 @@
From 6a185fdd49ee668c75ad7e95461de45c3a3d8d10 Mon Sep 17 00:00:00 2001
Author: Simon Kelley <simon@thekelleys.org.uk>
Date: Fri Apr 10 22:16:45 2026 +0100
Subject: [PATCH] Fix NSEC bitmap parsing infinite loop. CVE-2026-4890
Report from Royce M <royce@xchglabs.com>.
Location: dnssec.c:1290-1306, dnssec.c:1450-1463
The bitmap window iteration advances by p[1] instead of p[1]+2 (missing the 2-byte window header). With bitmap_length=0, both rdlen and p are
unchanged, causing an infinite loop and dnsmasq stops responding to all queries.
The same code accesses p[2] after only checking rdlen >= 2 without verifying p[1] >= 1, causing OOB reads at 6 locations.
Both bugs are reachable before RRSIG validation (confirmed by the source comment at line 2125), so no valid DNSSEC signatures are needed.
CVE: CVE-2026-4890
Upstream-Status: Backport [https://thekelleys.org.uk/dnsmasq/CVE/CVE-2026-4890.dnsmasq-2.91.diff]
Signed-off-by: Benjamin Robin <benjamin.robin@bootlin.com>
---
src/dnssec.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/src/dnssec.c b/src/dnssec.c
index ed2f53ff1763..68f1b5d0fab4 100644
--- a/src/dnssec.c
+++ b/src/dnssec.c
@@ -1270,10 +1270,10 @@ static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsi
packet checked to be as long as rdlen implies in prove_non_existence() */
/* If we can prove that there's no NS record, return that information. */
- if (nons && rdlen >= 2 && p[0] == 0 && (p[2] & (0x80 >> T_NS)) != 0)
+ if (nons && rdlen >= 2 && p[0] == 0 && p[1] >= 1 && (p[2] & (0x80 >> T_NS)) != 0)
*nons = 0;
- if (rdlen >= 2 && p[0] == 0)
+ if (rdlen >= 2 && p[0] == 0 && p[1] >= 1)
{
/* A CNAME answer would also be valid, so if there's a CNAME is should
have been returned. */
@@ -1301,8 +1301,8 @@ static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsi
break; /* finished checking */
}
- rdlen -= p[1];
- p += p[1];
+ rdlen -= p[1] + 2;
+ p += p[1] + 2;
}
return 0;
@@ -1429,7 +1429,7 @@ static int check_nsec3_coverage(struct dns_header *header, size_t plen, int dige
p += hash_len; /* skip next-domain hash */
rdlen -= p - psave;
- if (rdlen >= 2 && p[0] == 0)
+ if (rdlen >= 2 && p[0] == 0 && p[1] >= 1)
{
/* If we can prove that there's no NS record, return that information. */
if (nons && (p[2] & (0x80 >> T_NS)) != 0)
@@ -1458,8 +1458,8 @@ static int check_nsec3_coverage(struct dns_header *header, size_t plen, int dige
break; /* finished checking */
}
- rdlen -= p[1];
- p += p[1];
+ rdlen -= p[1] + 2;
+ p += p[1] + 2;
}
return 1;
--
2.55.0