CVE-2021-3178Network attack vector

File access beyond NFS subdirectory exports

Published Jan 19, 2021 · Updated Aug 3, 2024

Path traversal in Linux kernel NFSv3 through 5.10.8 allows remote authenticated users to access files outside a subdirectory export. The READDIRPLUS encoder in fs/nfsd/nfs3xdr.c returns file handles that permit traversal beyond the exported subdirectory instead of confining lookup to that export. Exposure requires a filesystem subdirectory export and existing permission within the NFS root mount; the classification is disputed because subtree checking is configurable.

CVSS severity6.5
Medium
EPSS probability2.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Path traversal in Linux kernel NFSv3 through 5.10.8 allows remote authenticated users to access files outside a subdirectory export. The READDIRPLUS encoder in fs/nfsd/nfs3xdr.c returns file handles that permit traversal beyond the exported subdirectory instead of confining lookup to that export. Exposure requires a filesystem subdirectory export and existing permission within the NFS root mount; the classification is disputed because subtree checking is configurable.

The record

CVE
CVE-2021-3178
Published
Jan 19, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-22, T1083
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5UbuntuCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
6.5NISTCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
6.0NISTAV:N/AC:L/Au:S/C:P/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1083File and Directory Discovery

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo