CVE-2021-27520

Exp

A cross-site scripting (XSS) issue in FUDForum 3.1.0 allows remote attackers to inject JavaScript via index.php in the "author" parameter.

Published: 2021-03-19 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-27520 is rated High Exploit Risk (76.4/100): CVSS Medium severity, with high exploitation likelihood (EPSS 6.40%, 93th percentile). 3 public exploit reference(s) are indexed (Exploit-DB). EPSS rose +4.58% over the last day, indicating growing attacker interest. 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-2021-27520

EDB-ID Source Kind Published Link
49943 exploit_db edb 2021-06-03 Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-27520

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 2026-06-15 1.81% 6.40% +4.58%
2 2026-03-11 1.25% 1.81% +0.57%
3 2026-03-10 — 1.25% —

Full EPSS history (24 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-27520

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-27520

Affected software / configurations for CVE-2021-27520

Vendor Product Version Raw CPE
fudforum fudforum 3.1.0 cpe:2.3:a:fudforum:fudforum:3.1.0:*:*:*:*:*:*:*

References for CVE-2021-27520

URL Tags
http://packetstormsecurity.com/files/162942/FUDForum-3.1.0-Cross-Site-Scripting.html Exploit Third Party Advisory VDB Entry
https://github.com/fudforum/FUDforum/issues/2 Exploit Issue Tracking Patch Third Party Advisory
cvelogic Threat Intelligence