CVE-2021-40978

Directory traversal in mkdocs

7.5 HighPublic exploitFix availableDisputed

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

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: None
Availability: None

Exploit likelihood

15.0%Up 14.4 points since Oct 8, 2021

What each source reports

NVD Score used 7.5

Record: CVE-2021-40978
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0: 5.0 MediumAV:N/AC:L/Au:N/C:P/I:N/A:N
Weakness: CWE-22
Updated: 2026-11-02

CVE List No score

Record: CVE-2021-40978
Updated: 2026-11-02

EUVDEUVD-2021-0136 No score

Record: EUVD-2021-0136
Updated: 2026-11-03

GitHub AdvisoriesGHSA-qh9q-34h6-hcv9 8.7

Directory traversal in mkdocs

The mkdocs 1.2.2 built-in dev-server allows directory traversal using the port 8000, enabling remote exploitation to obtain :sensitive information.

Record: GHSA-qh9q-34h6-hcv9
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness: CWE-12, CWE-22
Updated: 2026-11-02

OSV 7.5

Record: CVE-2021-40978
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated: 2026-11-02

OSVDEBIAN-CVE-2021-40978 7.5

Record: DEBIAN-CVE-2021-40978
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated: 2026-11-02

OSVGHSA-qh9q-34h6-hcv9 8.7

Directory traversal in mkdocs

The mkdocs 1.2.2 built-in dev-server allows directory traversal using the port 8000, enabling remote exploitation to obtain :sensitive information.

Record: GHSA-qh9q-34h6-hcv9
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness: CWE-12, CWE-22
Updated: 2026-11-02

OSVPYSEC-2021-878 7.5

Record: PYSEC-2021-878
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated: 2026-11-02

Affected products

mkdocs

Affected packages

Affected packages
Package	Affected	Fixed
`mkdocs` PyPI	1.2.2 to 1.2.2	1.2.3
`python-mkdocs` Debian:12	All versions, plus listed versions 1.4.2+dfsg-21.5.2+dfsg-11.5.3+dfsg-11.5.3+dfsg-21.6.1+dfsg-1 Show 7 moreShow less 1.6.1+dfsg-21.6.1+dfsg-31.6.1+dfsg1-11.6.1+dfsg1-21.6.1+dfsg1-31.6.1+dfsg1-41.6.1+dfsg1-5	None known
`python-mkdocs` Debian:13	All versions, plus listed versions 1.6.1+dfsg1-21.6.1+dfsg1-31.6.1+dfsg1-41.6.1+dfsg1-5	None known
`python-mkdocs` Debian:14	All versions, plus listed versions 1.6.1+dfsg1-21.6.1+dfsg1-31.6.1+dfsg1-41.6.1+dfsg1-5	None known
`mkdocs` PyPI	1.2.2 up to 1.2.3	1.2.3

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
Source	Link	Date
Nuclei	MKdocs 1.2.2 - Directory Traversal
PoC in GitHub	nisdn/CVE-2021-40978	2021-10-04

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, Nuclei, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-40978 is a high vulnerability (CVSS 7.5) in Mkdocs, published October 7, 2021. Its validity is disputed. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 15.0%, the 96th percentile. Fixed in mkdocs 1.2.3.

References

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