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CVE-2019-9955

43
FAUCET Score

CVE-2019-9955 is a Reflected Cross-Site Scripting (XSS) vulnerability affecting numerous Zyxel firewall and VPN devices, including various ATP, USG, and ZyWALL series. This medium-severity flaw (CVSS 6.1) allows an unauthenticated attacker to inject malicious scripts into the security firewall login page by manipulating the 'mp_idx' parameter, potentially leading to information disclosure or limited integrity compromise. While there is no evidence of active exploitation in the wild, public exploit code is available via ExploitDB and Nuclei templates, indicating a readily exploitable condition. Community discussion and media coverage for this CVE are minimal.

Impacted Technologies

VendorProductVersion(s)CPE
4.31CPE matchmatch criteria
cpe:2.3:o:zyxel:atp200_firmware:4.31:*:*:*:*:*:*:*
4.31CPE matchmatch criteria
cpe:2.3:o:zyxel:atp500_firmware:4.31:*:*:*:*:*:*:*
4.31CPE matchmatch criteria
cpe:2.3:o:zyxel:atp800_firmware:4.31:*:*:*:*:*:*:*
4.31CPE matchmatch criteria
cpe:2.3:o:zyxel:usg20-vpn_firmware:4.31:*:*:*:*:*:*:*
4.31CPE matchmatch criteria
cpe:2.3:o:zyxel:usg20w-vpn_firmware:4.31:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

6.1MEDIUM

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
2.7
CvssVersion
3.0

Exploit Intelligence

EPSS Score
20.86%
Probability of exploitation in next 30 days
EPSS Percentile
97.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Nuclei: CVE-2019-9955 · Jan 9, 2021
ExploitDB: EDB-46706 · Apr 16, 2019
This CVE's current EPSS score of 0.2086 is in the 99th percentile among its peer group of 26,234 CVEs.

Social Chatter

No social media mentions found for this CVE.

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

packetstormsecurity.com / files/152525/Zyxel-ZyWall-Cross-Site-Scripting.html
ExploitThird Party AdvisoryVDB Entry
seclists.org / fulldisclosure/2019/Apr/22
Mailing ListThird Party Advisory
exploit-db.com / exploits/46706
ExploitThird Party AdvisoryVDB Entry
securitymetrics.com / blog/Zyxel-Devices-Vulnerable-Cross-Site-Scripting-Login-page
PatchThird Party Advisory
zyxel.com / support/reflected-cross-site-scripting-vulnerability-of-firewalls.shtml
Vendor Advisory