high CVSS 7.8

CVE-2021-47293·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_skbmod: Skip non-Ethernet packets Currently tcf_skbmod_act() assumes that packets use Ethernet as their L2 protocol, which is not always the case. As an example, for CAN devices: $ ip link add dev vcan0 type vcan $ ip link set up vcan0 $ tc qdisc add dev vcan0 root handle 1: htb $ tc filter add dev vcan0 parent 1: protocol ip prio 10 \ matchall action skbmod swap mac Doing the above silently corrupts all the packets. Do not perform skbmod actions for non-Ethernet packets.

Severity
high
Software
Kernel
Fixed in
5.13.6
Published
2024-05-21

Affected versions

From: 5.11

Until: 5.13.6

Fixed in: 5.13.6

How to fix this CVE

Update your Linux kernel to version 5.13.6 or later to resolve this traffic classification vulnerability. The flaw caused the kernel's traffic shaping module (act_skbmod) to incorrectly process non-Ethernet packets (such as CAN frames), leading to silent packet corruption. Apply the kernel security update and reboot your system to complete remediation.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check the running kernel version with `uname -r` and compare against 5.13.6 or later
  2. Step 2: Verify if traffic control (tc) rules with skbmod actions are configured by running `tc filter show dev <interface>` on all network interfaces
  3. Step 3: Inspect system logs for packet corruption symptoms using `journalctl -u kernel --since='1 hour ago' | grep -i 'skb\|corruption\|mac'`
  4. Step 4: After updating, confirm the new kernel version with `uname -r` and test skbmod filters on non-Ethernet interfaces (CAN, etc.) to verify normal packet flow

FAQ

What is CVE-2021-47293?

This vulnerability is a logic error in the Linux kernel's traffic control skbmod action module, which blindly assumed all packets used Ethernet framing. When applied to non-Ethernet devices like CAN interfaces, it silently corrupted packet headers instead of skipping the operation.

Is CVE-2021-47293 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and has no public exploit code available. However, misconfigured traffic control rules could inadvertently trigger the flaw.

What versions of Kernel are affected by CVE-2021-47293?

Kernel versions 5.11 through 5.13.5 are vulnerable. The fix was released in 5.13.6 and has been backported to stable branches.

How do I check if my server is vulnerable to CVE-2021-47293?

Run `uname -r` to check your kernel version. If it reports 5.11.x through 5.13.5, you are vulnerable. Additionally, check if traffic control rules with skbmod actions target non-Ethernet interfaces using `tc filter show`.

Does Defensia detect CVE-2021-47293?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47293 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-43501CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps the next segment into ipv6_hdr->daddr, recompresses, then pulls the old header and pushes the new one plus the IPv6 header back. The recompressed header can be larger than the received one when the swap reduces the common-prefix length the segments share with daddr (CmprI=0, CmprE>0, seg[0][0] != daddr[0] gives the maximum +8 bytes). pskb_expand_head() was gated on segments_left == 0, so on earlier segments the push consumed unchecked headroom. Once skb_push() leaves fewer than skb->mac_len bytes in front of data, skb_mac_header_rebuild()'s call to: skb_set_mac_header(skb, -skb->mac_len); will store (data - head) - mac_len into the u16 mac_header field, which wraps to ~65530, and the following memmove() writes mac_len bytes ~64KiB past skb->head. A single AF_INET6/SOCK_RAW/IPV6_HDRINCL packet over lo with a two segment type-3 SRH (CmprI=0, CmprE=15) reaches headroom 8 after one pass; KASAN reports a 14-byte OOB write in ipv6_rthdr_rcv. Fix this by expanding the head whenever the remaining room is less than the push size plus mac_len, and request that much extra so the rebuilt MAC header fits afterwards.
CVE-2026-64216CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it is wanting to unlock and compares that to rreq->no_unlock_folio so that it doesn't unlock a folio being read for netfs_perform_write() or netfs_write_begin(). However, given that netfs_unlock_abandoned_read_pages() is called _after_ NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to dereference is the one specified by ->no_unlock_folio as ownership immediately reverts to the caller. Fix this by storing the folio pointer instead and using that rather than the index. Also fix netfs_unlock_read_folio() where the same applies.

References

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