CVE-2021-47107: Linux Kernel buffer overflow (CVSS 9.8)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

Linux Kernel≥ 5.13 < 5.15.12 · 5.16

Remediation

Fixed in

Linux Kernel≥ 5.15.12

Patch & vendor advisories

References

https://cert-portal.siemens.com/productcert/html/ssa-265688.html
https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72ExploitMailing ListPatch
https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1ExploitMailing ListPatch
https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885ExploitMailing ListPatch

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2021-47107 being actively exploited?

CVE-2021-47107 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.85%.

How severe is CVE-2021-47107?

CVE-2021-47107 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.85% probability of exploitation.

Which products are affected by CVE-2021-47107?

Affected products include Linux Kernel.

How do I fix CVE-2021-47107?

Upgrade affected software to a fixed version, for example Linux Kernel 5.15.12 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-47107 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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