high CVSS 7.8

CVE-2021-47357·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: atm: iphase: fix possible use-after-free in ia_module_exit() This module's remove path calls del_timer(). However, that function does not wait until the timer handler finishes. This means that the timer handler may still be running after the driver's remove function has finished, which would result in a use-after-free. Fix by calling del_timer_sync(), which makes sure the timer handler has finished, and unable to re-schedule itself.

Severity
high
Software
Kernel
Fixed in
5.13.3
Published
2024-05-21

Affected versions

From: 5.13

Until: 5.13.3

Fixed in: 5.13.3

How to fix this CVE

Update your Linux kernel to version 5.13.3 or later to resolve this use-after-free vulnerability in the ATM iphase driver module. The vulnerability occurs when the driver's removal routine fails to properly synchronize timer cleanup, allowing the timer handler to access freed memory. Apply the kernel update through your distribution's package manager and reboot your system to activate the patched kernel.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check the installed kernel version with `uname -r` and compare against 5.13.3 or later
  2. Step 2: Verify if the ATM iphase driver is loaded by running `lsmod | grep iphase` — if output appears, the vulnerable component is present
  3. Step 3: Search kernel logs for timer-related crashes using `sudo dmesg | grep -i 'timer\|iphase\|use-after-free'` or check `/var/log/kern.log` for memory corruption errors
  4. Step 4: After kernel update and reboot, confirm the new version with `uname -r` and verify the iphase module still loads without errors using `sudo modprobe iphase && lsmod | grep iphase`

FAQ

What is CVE-2021-47357?

CVE-2021-47357 is a use-after-free vulnerability in the Linux kernel's ATM iphase driver where improper timer cleanup during module removal allows the timer handler to execute and access already-freed kernel memory, potentially causing system crashes or code execution.

Is CVE-2021-47357 being actively exploited?

No, CVE-2021-47357 is not listed as actively exploited in the CISA Known Exploited Vulnerabilities catalog, and no public exploits are currently available.

What versions of Kernel are affected by CVE-2021-47357?

Linux kernel versions 5.13 through 5.13.2 are affected; the vulnerability is fixed in kernel 5.13.3 and later stable releases.

How do I check if my server is vulnerable to CVE-2021-47357?

Run `uname -r` to check your kernel version — if it shows 5.13.0 through 5.13.2, your system is vulnerable. Additionally, run `lsmod | grep iphase` to confirm the ATM iphase driver is loaded.

Does Defensia detect CVE-2021-47357?

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-2021-47357 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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