Public proof of conceptFix available

CVE-2021-31800

A public proof of concept exists; no exploitation attested.

Published2021-05-05
WeaknessCWE-22

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Multiple path traversal vulnerabilities exist in smbserver.py in Impacket through 0.9.22. An attacker that connects to a running smbserver instance can list and write to arbitrary files via ../ directory traversal. This could potentially be abused to achieve arbitrary code execution by replacing /etc/shadow or an SSH authorized key.

Timeline

dates in UTC

2021-05-0511:15CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub
2026-10-2319:23EPSS crossed 10 %FIRST EPSS

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-31800?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-31800?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Fedoraproject fedora

Branch	Affected	Fixed in	Source
32.x	= 32	no fix published	NVD
33.x	= 33	no fix published	NVD
34.x	= 34	no fix published	NVD

Secureauth impacket

Branch	Affected	Fixed in	Source
0.9	≤ 0.9.22	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

github.comPatch
github.comRelease Notes

Detection

read 2026-10-23 19:23 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 2 repositories, unverifiedp0dalirius/CVE-2021-31800-Impacket-SMB-Server-Arbitrary-file-read-writeLouzogh/CVE-2021-31800

Sources

NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.07.5read 2026-10-23
NVDweakness (CWE)CWE-22read 2026-10-23
FIRST EPSSEPSS score19.4 %read 2026-10-23
PoC-in-GitHubproof of concept2read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2021-05-05
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-31800?

Is CVE-2021-31800 actively exploited?

Active exploitation of CVE-2021-31800 has not been confirmed. Its EPSS score was 19.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-31800?

CVE-2021-31800 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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