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Fencer Vulns
high 7.5

CVE-2017-7783 in the critical feed json

If a long user name is used in a username/password combination in a site URL (such as " http://UserName:Password@example.com"), the resulti…

published 2018-06-11 8 y ago modified 2026-06-17 4 mo ago also EUVD-2017-16758

cvss
7.5
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
13.8%
EPSS 13.8% chance of exploitation in 30 days, percentile 96%
public exploits
1
Exploit-DB

Summary

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.

Patch / fix

  • Mozilla Firefox 55
  • firefox Ubuntu 14.04 LTS 55.0.1+build2-0ubuntu0.14.04.2
  • firefox Ubuntu 16.04 LTS 55.0.1+build2-0ubuntu0.16.04.2

ubuntu advisories UBUNTU-CVE-2017-7783

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1

  • firefox Arch Linux 55.0-1

arch linux advisories AVG-375

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2017-7783 updated cvss 7.5

Mozilla: DOS attack through long username in URL (MFSA 2017-18)

  • Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Timeline

  1. First public exploit (EDB-43020)
  2. Published

Exploit prediction

13.85% chance of exploitation in the next 30 days, higher than 96% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • EDB-43020 Mozilla Firefox < 55 - Denial of Service dos, 2017-10-20
  • bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1360842 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.0 7.5 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • Mozilla Firefox

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.