Linux Kernel up to 5.18.2 compat_arm_syscall privilege escalation

Summaryinfo

A vulnerability was found in Linux Kernel up to 5.4.197/5.10.120/5.15.45/5.17.13/5.18.2 and classified as problematic. The impacted element is the function compat_arm_syscall. The manipulation results in an unknown weakness. This vulnerability is cataloged as CVE-2022-49520. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Linux Kernel up to 5.4.197/5.10.120/5.15.45/5.17.13/5.18.2. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: arm64: compat: Do not treat syscall number as ESR_ELx for a bad syscall If a compat process tries to execute an unknown system call above the __ARM_NR_COMPAT_END number, the kernel sends a SIGILL signal to the offending process. Information about the error is printed to dmesg in compat_arm_syscall() -> arm64_notify_die() -> arm64_force_sig_fault() -> arm64_show_signal(). arm64_show_signal() interprets a non-zero value for current->thread.fault_code as an exception syndrome and displays the message associated with the ESR_ELx.EC field (bits 31:26). current->thread.fault_code is set in compat_arm_syscall() -> arm64_notify_die() with the bad syscall number instead of a valid ESR_ELx value. This means that the ESR_ELx.EC field has the value that the user set for the syscall number and the kernel can end up printing bogus exception messages*. For example, for the syscall number 0x68000000, which evaluates to ESR_ELx.EC value of 0x1A (ESR_ELx_EC_FPAC) the kernel prints this error: [ 18.349161] syscall[300]: unhandled exception: ERET/ERETAA/ERETAB, ESR 0x68000000, Oops - bad compat syscall(2) in syscall[10000+50000] [ 18.350639] CPU: 2 PID: 300 Comm: syscall Not tainted 5.18.0-rc1 #79 [ 18.351249] Hardware name: Pine64 RockPro64 v2.0 (DT) [..] which is misleading, as the bad compat syscall has nothing to do with pointer authentication. Stop arm64_show_signal() from printing exception syndrome information by having compat_arm_syscall() set the ESR_ELx value to 0, as it has no meaning for an invalid system call number. The example above now becomes: [ 19.935275] syscall[301]: unhandled exception: Oops - bad compat syscall(2) in syscall[10000+50000] [ 19.936124] CPU: 1 PID: 301 Comm: syscall Not tainted 5.18.0-rc1-00005-g7e08006d4102 #80 [ 19.936894] Hardware name: Pine64 RockPro64 v2.0 (DT) [..] which although shows less information because the syscall number, wrongfully advertised as the ESR value, is missing, it is better than showing plainly wrong information. The syscall number can be easily obtained with strace. *A 32-bit value above or equal to 0x8000_0000 is interpreted as a negative integer in compat_arm_syscal() and the condition scno < __ARM_NR_COMPAT_END evaluates to true; the syscall will exit to userspace in this case with the ENOSYS error code instead of arm64_notify_die() being called.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2022-49520 since 02/26/2025. The exploitability is told to be easy. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 241018 (EulerOS 2.0 SP13 : kernel (EulerOS-SA-2025-1704)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.4.198, 5.10.121, 5.15.46, 5.17.14 or 5.18.3 eliminates this vulnerability. Applying the patch efd183d988b416fcdf6f7c298a17ced4859ca77d/ad97425d23af3c3b8d4f6a2bb666cb485087c007/621916afe8cd4f322eb12759b64a2f938d4e551d/095e975f8150ccd7f852eb578c1cdbdd2f517c7a/3910ae71cb963fa2b68e684489d4fc3d105afda0/3fed9e551417b84038b15117732ea4505eee386b is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (241018). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.4.197
• 5.10.120
• 5.15.0
• 5.15.1
• 5.15.2
• 5.15.3
• 5.15.4
• 5.15.5
• 5.15.6
• 5.15.7
• 5.15.8
• 5.15.9
• 5.15.10
• 5.15.11
• 5.15.12
• 5.15.13
• 5.15.14
• 5.15.15
• 5.15.16
• 5.15.17
• 5.15.18
• 5.15.19
• 5.15.20
• 5.15.21
• 5.15.22
• 5.15.23
• 5.15.24
• 5.15.25
• 5.15.26
• 5.15.27
• 5.15.28
• 5.15.29
• 5.15.30
• 5.15.31
• 5.15.32
• 5.15.33
• 5.15.34
• 5.15.35
• 5.15.36
• 5.15.37
• 5.15.38
• 5.15.39
• 5.15.40
• 5.15.41
• 5.15.42
• 5.15.43
• 5.15.44
• 5.15.45
• 5.17.0
• 5.17.1
• 5.17.2
• 5.17.3
• 5.17.4
• 5.17.5
• 5.17.6
• 5.17.7
• 5.17.8
• 5.17.9
• 5.17.10
• 5.17.11
• 5.17.12
• 5.17.13
• 5.18.0
• 5.18.1
• 5.18.2

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Sourcesinfo

Entryinfo

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