Vulnerability Details : CVE-2021-47036
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
Products affected by CVE-2021-47036
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Exploit prediction scoring system (EPSS) score for CVE-2021-47036
0.04%
Probability of exploitation activity in the next 30 days
EPSS Score History
~ 7 %
Percentile, the proportion of vulnerabilities that are scored at or less
CVSS scores for CVE-2021-47036
Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source | First Seen |
---|---|---|---|---|---|---|
5.5
|
MEDIUM | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
1.8
|
3.6
|
NIST | 2025-01-10 |
References for CVE-2021-47036
-
https://git.kernel.org/stable/c/450687386cd16d081b58cd7a342acff370a96078
udp: skip L4 aggregation for UDP tunnel packets - kernel/git/stable/linux.git - Linux kernel stable treePatch
-
https://git.kernel.org/stable/c/18f25dc399901426dff61e676ba603ff52c666f7
udp: skip L4 aggregation for UDP tunnel packets - kernel/git/stable/linux.git - Linux kernel stable treePatch
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