CVE-2021-47107: linux kernel Buffer Overflow

Description

In the Linux kernel, the following vulnerability has been resolved: NFSD: Fix READDIR buffer overflow If a client sends a READDIR count argument that is too small (say, zero), then the buffer size calculation in the new init_dirlist helper functions results in an underflow, allowing the XDR stream functions to write beyond the actual buffer. This calculation has always been suspect. NFSD has never sanity- checked the READDIR count argument, but the old entry encoders managed the problem correctly. With the commits below, entry encoding changed, exposing the underflow to the pointer arithmetic in xdr_reserve_space(). Modern NFS clients attempt to retrieve as much data as possible for each READDIR request. Also, we have no unit tests that exercise the behavior of READDIR at the lower bound of @count values. Thus this case was missed during testing.

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-120 CWE-120

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.13 — 5.15.12
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72 https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1 https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885 https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72 https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1 https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885

Exploits

https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72 https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1 https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885 https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72 https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1 https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885

Other References

https://cert-portal.siemens.com/productcert/html/ssa-265688.html

Frequently Asked Questions

What is CVE-2021-47107? +

In the Linux kernel, the following vulnerability has been resolved: NFSD: Fix READDIR buffer overflow If a client sends a READDIR count argument that is too small (say, zero), then the buffer size calculation in the new init_dirlist helper functions results in an underflow, allowing the XDR stream functions to write beyond the actual buffer. This calculation has always been suspect. NFSD has never sanity- checked the READDIR count argument, but the old entry encoders managed the problem correctly. With the commits below, entry encoding changed, exposing the underflow to the pointer arithmetic in xdr_reserve_space(). Modern NFS clients attempt to retrieve as much data as possible for each READDIR request. Also, we have no unit tests that exercise the behavior of READDIR at the lower bound of @count values. Thus this case was missed during testing. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2021-47107? +

CVE-2021-47107 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2021-47107? +

CVE-2021-47107 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47107? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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