Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
Linux Linux — udp: skip L4 aggregation for UDP tunnel packets
AV AC PR UI S C I A CVSS EPSS %ile KEV
L L L N U N N H 5.5 .0053 42.6 —
AFFECTED
Product Versions Fixed
Linux 9fd1ff5d2ac7181844735806b0a703c942365291 – —
Linux 5.6 – 5.12.4
TIMELINE
Feb 27 Reserved by Linux
Feb 28 Published (CNA: Linux)
Aug 4 RESCORED — CVE-2021-47036 (Linux). CVSS 9.8 → 5.5 (NVD).
Description
In the Linux kernel, the following vulnerability has been resolved:
udp: skip L4 aggregation for UDP tunnel packets
If NETIF_F_GRO_FRAGLIST or NETIF_F_GRO_UDP_FWD are enabled, and there
are UDP tunnels available in the system, udp_gro_receive() could end-up
doing L4 aggregation (either SKB_GSO_UDP_L4 or SKB_GSO_FRAGLIST) at
the outer UDP tunnel level for packets effectively carrying and UDP
tunnel header.
That could cause inner protocol corruption. If e.g. the relevant
packets carry a vxlan header, different vxlan ids will be ignored/
aggregated to the same GSO packet. Inner headers will be ignored, too,
so that e.g. TCP over vxlan push packets will be held in the GRO
engine till the next flush, etc.
Just skip the SKB_GSO_UDP_L4 and SKB_GSO_FRAGLIST code path if the
current packet could land in a UDP tunnel, and let udp_gro_receive()
do GRO via udp_sk(sk)->gro_receive.
The check implemented in this patch is broader than what is strictly
needed, as the existing UDP tunnel could be e.g. configured on top of
a different device: we could end-up skipping GRO at-all for some packets.
Anyhow, that is a very thin corner case and covering it will add quite
a bit of complexity.
v1 -> v2:
- hopefully clarify the commit message
Lifecycle
Complete event history — 3 events, chronological
| Date | Event | Detail |
| February 27, 2024 | Reserved | Reserved by Linux |
| February 28, 2024 | Published | Published (CNA: Linux) |
| August 4, 2026 | RESCORED | RESCORED — CVE-2021-47036 (Linux). CVSS 9.8 → 5.5 (NVD). |
Affected
Affected products and packages — 2 rows
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
| Linux | Linux | — | 9fd1ff5d2ac7181844735806b0a703c942365291 | — |
| Linux | Linux | — | 5.6 | 5.12.4 |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2021-47036 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.