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Public proof of conceptFix available

CVE-2021-40978

A public proof of concept exists; no exploitation attested.

  • Published2021-10-07
  • 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

The mkdocs 1.2.2 built-in dev-server allows directory traversal using the port 8000, enabling remote exploitation to obtain :sensitive information. NOTE: the vendor has disputed this as described in https://github.com/mkdocs/mkdocs/issues/2601.] and https://github.com/nisdn/CVE-2021-40978/issues/1

Timeline

dates in UTC
  1. 2021-10-0714:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 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-2021-40978?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-40978?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Mkdocs
BranchAffectedFixed in
1.2= 1.2.2no fix published
mkdocs
BranchAffectedFixed in
1.2≥ 1.2.2, < 1.2.31.2.3

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

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • python-mkdocsDebian:14all versions · no fixed version listed
  • python-mkdocsDebian:13all versions · no fixed version listed
  • python-mkdocsDebian:12all versions · no fixed version listed

Vendor advisories

  • CVE-2021-40978 Red Hat Product Security

    mkdocs: Directory traversal in dev-server

Full record on NVD

Fix

  1. Workaround from the vendor Red Hat Product Security CVE-2021-40978 · 1 productThe built-in dev-serve is known to not be secure and should not be used in a sensitive environment. Users should use it only as a development server.

Detection

read 2026-11-02 22:42 UTC
Nuclei template
available
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiednisdn/CVE-2021-40978
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Published
2021-10-07
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-qh9q-34h6-hcv9

Frequently asked questions

What is CVE-2021-40978?

The mkdocs 1.2.2 built-in dev-server allows directory traversal using the port 8000, enabling remote exploitation to obtain :sensitive information. NOTE: the vendor has disputed this as described in https://github.com/mkdocs/mkdocs/issues/2601.] and https://github.com/nisdn/CVE-2021-40978/issues/1

Is CVE-2021-40978 actively exploited?

A proof-of-concept exploit exists for CVE-2021-40978, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2021-40978?

CVE-2021-40978 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

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Sources for this record