CVE-2021-40978

Exp

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

Published: 2021-10-07 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40978 is rated High Exploit Risk (78.4/100): CVSS High severity, with high exploitation likelihood (EPSS 79.72%, 99th percentile). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-40978

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-40978

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-06 81.01% 79.72% -1.29%
2 2026-05-02 84.81% 81.01% -3.81%
3 2025-11-21 — 84.81% —

Full EPSS history (29 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40978

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-40978

GitHub Security Advisory for CVE-2021-40978

OS Trackers for CVE-2021-40978

vendor priority summary link
debian unimportant CVE-2021-40978 unimportant priority: Debian including 1 source packages (python-mkdocs), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 5. https://security-tracker.debian.org/tracker/CVE-2021-40978
ubuntu medium CVE-2021-40978 medium priority: Ubuntu including 1 source packages (python-mkdocs), 12 status rows across 12 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, trusty, upstream, xenial): not-affected 10, DNE 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-40978

Affected software / configurations for CVE-2021-40978

Vendor Product Version Raw CPE
mkdocs mkdocs 1.2.2 cpe:2.3:a:mkdocs:mkdocs:1.2.2:*:*:*:*:*:*:*

References for CVE-2021-40978

URL Tags
https://github.com/mkdocs/mkdocs Third Party Advisory
https://github.com/mkdocs/mkdocs/issues/2601 Issue Tracking Third Party Advisory
https://github.com/nisdn/CVE-2021-40978 Exploit Third Party Advisory
https://github.com/nisdn/CVE-2021-40978/issues/1 Issue Tracking Third Party Advisory
cvelogic Threat Intelligence