CVE-2021-46933
7.8 · HIGHOverview
CVE-2021-46933 is a high-severity vulnerability affecting linux linux_kernel. It was published on February 27, 2024 and has a CVSS 3.1 base score of 7.8 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.8, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
Technical Description
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.
ffs_data_clear is indirectly called from both ffs_fs_kill_sb and
ffs_ep0_release, so it ends up being called twice when userland closes ep0
and then unmounts f_fs.
If userland provided an eventfd along with function's USB descriptors, it
ends up calling eventfd_ctx_put as many times, causing a refcount
underflow.
NULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.
Also, set epfiles to NULL right after de-allocating it, for readability.
For completeness, ffs_data_clear actually ends up being called thrice, the
last call being before the whole ffs structure gets freed, so when this
specific sequence happens there is a second underflow happening (but not
being reported):
/sys/kernel/debug/tracing# modprobe usb_f_fs
/sys/kernel/debug/tracing# echo ffs_data_clear > set_ftrace_filter
/sys/kernel/debug/tracing# echo function > current_tracer
/sys
Remediation
Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| linux | linux_kernel | >= 4.0.0, < 4.4.298 | Affected |
References
Frequently Asked Questions
What is CVE-2021-46933?
CVE-2021-46933 is a high-severity vulnerability affecting linux linux_kernel. It was published on February 27, 2024 and has a CVSS 3.1 base score of 7.8 (HIGH).
How severe is CVE-2021-46933?
This vulnerability has a CVSS 3.1 base score of 7.8, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2021-46933?
Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2021-46933?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-46933 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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