high CVSS 7.8 EPSS <0.1%

CVE-2021-47520·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: can: pch_can: pch_can_rx_normal: fix use after free After calling netif_receive_skb(skb), dereferencing skb is unsafe. Especially, the can_frame cf which aliases skb memory is dereferenced just after the call netif_receive_skb(skb). Reordering the lines solves the issue.

Severity
high
Software
Kernel
Fixed in
5.15.8
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 4% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2021-47520 scores 7.8 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 5.11

Until: 5.15.8

Fixed in: 5.15.8

How to fix this CVE

Update your Linux kernel to version 5.15.8 or later to patch a use-after-free vulnerability in the PCH CAN driver that could lead to memory corruption. This issue occurs when the kernel attempts to access CAN frame data after the network buffer has been freed by netif_receive_skb(). Apply the kernel update immediately and reboot your system to activate the patched version.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your current kernel version: uname -r — compare against 5.15.8; versions 5.11 through 5.15.7 are vulnerable
  2. Verify PCH CAN driver is loaded: lsmod | grep pch_can — if present, your system uses the affected driver
  3. Review dmesg for memory-related errors: dmesg | grep -i 'use after free\|kernel panic\|segfault' — these may indicate exploitation attempts
  4. Confirm the fix was applied post-reboot: uname -r should show 5.15.8 or higher, and compare file checksums: sha256sum /boot/vmlinuz-$(uname -r)

FAQ

What is CVE-2021-47520?

CVE-2021-47520 is a use-after-free vulnerability in the Linux kernel's PCH CAN controller driver where the kernel dereferences freed memory after passing a network buffer to the network stack, potentially causing memory corruption or kernel panic.

Is CVE-2021-47520 being actively exploited?

No, CVE-2021-47520 is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are available, though the vulnerability has high severity due to its local privilege escalation potential.

What versions of Kernel are affected by CVE-2021-47520?

Linux kernel versions 5.11 through 5.15.7 are vulnerable; kernel 5.15.8 and later contain the fix.

How do I check if my server is vulnerable to CVE-2021-47520?

Run uname -r and verify the version is between 5.11 and 5.15.7; if it is and lsmod | grep pch_can returns results, your system is vulnerable.

Does Defensia detect CVE-2021-47520?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47520 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-53151CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix the ACK parser to extract the SACK table for parsing Fix modification of the received skbuff in rxrpc_input_soft_acks() and a potential incorrect access of the buffer in a fragmented UDP packet (the packet would probably have to be deliberately pre-generated as fragmented) when AF_RXRPC tries to extract the contents of the SACK table by copying out the contents of the SACK table into a buffer before attempting to parse AF_RXRPC assumes that it can just call skb_condense() and then validly access the SACK table from skb->data and that it will be a flat buffer - but skb_condense() can silently fail to do anything under some circumstances. Note that whilst rxrpc_input_soft_acks() should be able to parse extended ACKs, the rest of AF_RXRPC doesn't currently support that. Further, there's then no need to call skb_condense() in rxrpc_input_ack(), so don't.
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CVE-2026-53228CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: sit: reload inner IPv6 header after GSO offloads ipip6_tunnel_xmit() caches the inner IPv6 header pointer at function entry and continues using it after iptunnel_handle_offloads(). For GSO skbs, iptunnel_handle_offloads() calls skb_header_unclone(). When the skb header is cloned, skb_header_unclone() can call pskb_expand_head(), which may move the skb head. The pskb_expand_head() contract requires pointers into the skb header to be reloaded after the call. If the later skb_realloc_headroom() branch is not taken, SIT uses the stale iph6 pointer to read the inner hop limit and DS field. That can read from a freed skb head after the old head's remaining clone is released. Reload iph6 after the offload helper succeeds and before subsequent reads from the inner IPv6 header. Keep the existing reload after skb_realloc_headroom(), since that branch can also replace the skb.

References

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