CVE-2017-7783

HIGH

Firefox < 55.0 - Denial of Service via Long Username in URL Authentication Prompt

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2017-7783. PoCs published by Amit Sangra.

AI-analyzed exploit summary This exploit leverages a denial of service vulnerability in Mozilla Firefox < 55 by crafting a URL with an excessively long username, causing the browser to hang or crash. The PoC forces the victim to view attacker-supplied content before triggering the DoS.

Description

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

Exploits (1)

exploitdb WORKING POC VERIFIED
by Amit Sangra · textdosmultiple
https://www.exploit-db.com/exploits/43020

This exploit leverages a denial of service vulnerability in Mozilla Firefox < 55 by crafting a URL with an excessively long username, causing the browser to hang or crash. The PoC forces the victim to view attacker-supplied content before triggering the DoS.

Classification
Working Poc 90%
Attack Type
Dos
Complexity
Trivial
Reliability
Reliable
Target: Mozilla Firefox < 55
No auth needed
Prerequisites: Victim must visit a malicious webpage
devstral-2 · analyzed Feb 16, 2026 Full analysis →

References (5)

Core 5
Core References
Third Party Advisory, VDB Entry vdb-entry x_refsource_bid
http://www.securityfocus.com/bid/100401
Exploit, Issue Tracking, Patch x_refsource_confirm
https://bugzilla.mozilla.org/show_bug.cgi?id=1360842
Vendor Advisory x_refsource_confirm
https://www.mozilla.org/security/advisories/mfsa2017-18/
Third Party Advisory, VDB Entry exploit x_refsource_exploit-db
https://www.exploit-db.com/exploits/43020/
Third Party Advisory, VDB Entry vdb-entry x_refsource_sectrack
http://www.securitytracker.com/id/1039124

Scores

CVSS v3 7.5
EPSS 0.1370
EPSS Percentile 96.0%
Attack Vector NETWORK
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Details

CWE
CWE-20
Status published
Products (1)
mozilla/firefox < 55.0
Published Jun 11, 2018
Tracked Since Feb 18, 2026