What is CVE-2021-20837?

CVE-2021-20837 is a critical-severity vulnerability in Sixapart Movable Type, classified under OS Command Injection. CVSS score: 9.8/10. Published 2021-10-26.

How severe is CVE-2021-20837?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-20837 known to be exploited?

28 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

RCE in Sixapart Movable Type

CVE-2021-20837

Movable Type 7 r.5002 and earlier (Movable Type 7 Series), Movable Type 6.8.2 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.5002 and earlier (Movable Type Advanced 7 Series), Movable Type Advanced 6.8.2 and earlier (Movable Type Advanced 6 Series), Movable Type Premium 1.46 and earlier, and Movable Type Premium Advanced 1.46 and earlier allow remote attackers to execute arbitrary OS commands via unspecified vectors. Note that all versions of Movable Type 4.0 or later including unsupported (End-of-Life, EOL) versions are also affected by this vulnerability.

Vulnerability class: Command Injection (OS Command Injection)

EPSS: 0.881 (99.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Sixapart Movable_type
Six Apart Ltd. Movable Type — versions Movable Type 7 r.5002 and earlier (Movable Type 7 Series), Movable Type 6.8.2 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.5002 and earlier (Movable Type Advanced 7 Series), Movable Type Advanced 6.8.2 and earlier (Movable Type Advanced 6 Series), Movable Type Premium 1.46 and earlier, and Movable Type Premium Advanced 1.46 and earlier

Weakness classification (CWE)

CWE-78 — OS Command Injection

Public proof-of-concept exploits

References

vultures@jpcert.or.jp (x_refsource_MISC, Release Notes, Vendor Advisory)
vultures@jpcert.or.jp (Third Party Advisory, x_refsource_MISC)
vultures@jpcert.or.jp (Exploit, VDB Entry, Third Party Advisory, x_refsource_MISC)
vultures@jpcert.or.jp (VDB Entry, Third Party Advisory, x_refsource_MISC)

Frequently asked questions

What is CVE-2021-20837?: CVE-2021-20837 is a critical-severity vulnerability in Sixapart Movable Type, classified under OS Command Injection. CVSS score: 9.8/10. Published 2021-10-26.
How severe is CVE-2021-20837?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-20837 known to be exploited?: 28 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.