What’s Vulnerable › Vulnerabilities

CVE-2017-7783

• Severity: high (CVSS 7.5 v3.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 13.8% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2018-06-11 · updated 2026-06-17
• Weakness: CWE-20

Description

If a long user name is used in a username/password combination in a site URL (such as " http://UserName:Password@example.com"), the resulting modal prompt will hang in a non-responsive state or crash, causing a denial of service. This vulnerability affects Firefox < 55.

Affected products

• Mozilla Firefox: before 55.0 — fixed in 55.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 55.0. Check the vendor advisory for mitigations.

References

• http://www.securityfocus.com/bid/100401
• http://www.securitytracker.com/id/1039124
• https://bugzilla.mozilla.org/show_bug.cgi?id=1360842
• https://www.exploit-db.com/exploits/43020/
• https://www.mozilla.org/security/advisories/mfsa2017-18/
• http://www.securityfocus.com/bid/100401
• http://www.securitytracker.com/id/1039124
• https://bugzilla.mozilla.org/show_bug.cgi?id=1360842
• https://www.exploit-db.com/exploits/43020/
• https://www.mozilla.org/security/advisories/mfsa2017-18/

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