Re: [oe] [scarthgap][meta-networking][PATCH v2] dnsmasq: fix CVE-2026-4890

Hi,

On Wed, Jul 1, 2026 at 8:55 PM Benjamin Robin via
lists.openembedded.org
<[email protected]> wrote:
>
> 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).
>
> Signed-off-by: Benjamin Robin (Schneider Electric) <[email protected]>
> ---
> This patch needs to be applied on top of the previous CVE-2026-2291 patch
> ---
> Changes in v2:
> - Fix email subject
> - Link to v1: https://patch.msgid.link/[email protected]
> ---
>  .../recipes-support/dnsmasq/dnsmasq_2.90.bb        |  1 +
>  .../dnsmasq/files/CVE-2026-4890.patch              | 74 ++++++++++++++++++++++

This doesn't apply.

patching file src/dnssec.c
Hunk #1 FAILED at 1270.
Hunk #2 FAILED at 1301.
Hunk #3 succeeded at 1433 (offset 4 lines).
Hunk #4 FAILED at 1458.
3 out of 4 hunks FAILED -- rejects in file src/dnssec.c
Patch CVE-2026-4890.patch does not apply (enforce with -f)

The final patch merged upstream for this seems different from this
earlier version. But, it'd be good to mention source as:
https://thekelleys.org.uk/dnsmasq/CVE/CVE-2026-4890.dnsmasq-2.91.diff

>  2 files changed, 75 insertions(+)
>
> diff --git a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb
> index 3a7af56c34d7..ad79a3bfa828 100644
> --- a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb
> +++ b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.90.bb
> @@ -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"
>
> diff --git a/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4890.patch b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4890.patch
> new file mode 100644
> index 000000000000..1c60ae0b798f
> --- /dev/null
> +++ b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4890.patch
> @@ -0,0 +1,74 @@
> +From 12e5ee3495842ededf8057758ef8da59745bbf33 Mon Sep 17 00:00:00 2001
> +From: Simon Kelley <[email protected]>
> +Date: Fri, 10 Apr 2026 22:16:45 +0100
> +Subject: [PATCH] Fix NSEC bitmap parsing infinite loop. CVE-2026-4890
> +
> +Report from Royce M <[email protected]>.
> +
> +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://sources.debian.org/src/dnsmasq/2.90-4~deb12u2/debian/patches/CVE-2026-4890.patch]
> +
> +Signed-off-by: Benjamin Robin <[email protected]>
> +---
> + src/dnssec.c | 14 +++++++-------
> + 1 file changed, 7 insertions(+), 7 deletions(-)
> +
> +diff --git a/src/dnssec.c b/src/dnssec.c
> +index ed2f53ff..68f1b5d0 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;
> +--
> +2.43.0
>
> ---
> base-commit: b0c2c648a1af89e7a8dd4c2ec841f3bc0ed0ccb9
> change-id: 20260701-dnsmasq-cve-2026-4890-f5b3a76de3ad
> prerequisite-change-id: 20260701-dnsmasq-cve-2026-2291-fc2db33dde8d:v1
> prerequisite-patch-id: e7e3fdcabd23649336d34bd2f492f09007d73472
>
> Best regards,
> --
> Benjamin Robin (Schneider Electric) <[email protected]>
>
>
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