What is CVE-2021-27335?

CVE-2021-27335 is a critical-severity vulnerability in Kollectapp Kollect, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-02-18.

How severe is CVE-2021-27335?

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

Deserialization in Kollectapp Kollect

CVE-2021-27335

KollectApps before 4.8.16c is affected by insecure Java deserialization, leading to Remote Code Execution via a ysoserial.payloads.CommonsCollections parameter.

Vulnerability class: Insecure Deserialization

Published 2021-02-18 · last modified 2026-06-17.

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.

EPSS exploit prediction

EPSS: 0.030 (87.0th percentile), scored 2026-10-08.

Low probability of exploitation in the next 30 days, but still tracked. 87th percentile — 87.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.030 · newest: 0.030 · change: 0.000

Affected products

Kollectapp Kollect

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

hacked0x90.net/index.php/2021/02/15/kollectapp-insecure-java-deserialization/ (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-27335?: CVE-2021-27335 is a critical-severity vulnerability in Kollectapp Kollect, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2021-02-18.
How severe is CVE-2021-27335?: Critical severity. CVSS v3 base score is 9.8 out of 10.