medium CVSS 6.2 EPSS <0.1%

CVE-2021-47244·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: mptcp: Fix out of bounds when parsing TCP options The TCP option parser in mptcp (mptcp_get_options) could read one byte out of bounds. When the length is 1, the execution flow gets into the loop, reads one byte of the opcode, and if the opcode is neither TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the length of 1. This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack out of bounds when parsing TCP options.").

Severity
medium
Software
Kernel
Fixed in
5.12.13
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 22% 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.

Affected versions

From: 5.11

Until: 5.12.13

Fixed in: 5.12.13

How to fix this CVE

Update your Linux kernel to version 5.12.13 or later to patch a boundary condition in the MPTCP TCP option parser that could read beyond allocated memory. This vulnerability affects kernels from 5.11 through 5.12.12 and requires a kernel upgrade followed by a system reboot to take effect.

sudo dnf check-update kernel && sudo dnf update kernel

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'uname -r' to retrieve your current kernel version and confirm it falls within the 5.11 to 5.12.12 range
  2. Check dmesg logs for any memory access warnings or kernel panics related to TCP option parsing: 'sudo dmesg | grep -i "tcp\|option"'
  3. Verify MPTCP is enabled on your system by checking: 'cat /boot/config-$(uname -r) | grep CONFIG_MPTCP'
  4. After patching, reboot and confirm the new kernel version is loaded: 'uname -r' should show 5.12.13 or later

FAQ

What is CVE-2021-47244?

This vulnerability is an out-of-bounds read in the MPTCP subsystem's TCP option parsing function that occurs when processing malformed TCP option headers. The parser could read one additional byte beyond the declared option length under specific conditions, potentially causing a kernel crash or information disclosure.

Is CVE-2021-47244 being actively exploited?

No, there is no evidence of active exploitation in the wild, and no public exploits are currently available. This is primarily a kernel stability issue rather than a remote code execution vector.

What versions of Kernel are affected by CVE-2021-47244?

Linux kernel versions 5.11 through 5.12.12 are vulnerable. Version 5.12.13 and later versions contain the fix.

How do I check if my server is vulnerable to CVE-2021-47244?

Run 'uname -r' and check if the output shows a kernel version between 5.11 and 5.12.12 (inclusive). If your version is 5.12.13 or higher, you are patched.

Does Defensia detect CVE-2021-47244?

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-2021-47244 will appear in your dashboard with remediation steps.

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References

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