What is CVE-2017-7783?

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.

How severe is CVE-2017-7783?

CVE-2017-7783 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2017-7783 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 14% (96th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2017-7783?

CVE-2017-7783 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2017-7783?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2017-7783 published?

CVE-2017-7783 was published on 2018-06-11 and last updated on 2026-06-17.

CVE-2017-7783

Q: How severe is CVE-2017-7783?

CVE-2017-7783 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Q: Is CVE-2017-7783 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 14% (96th percentile), an estimate of the probability of exploitation in the next 30 days.

Q: What products are affected by CVE-2017-7783?

CVE-2017-7783 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

Q: How do I fix CVE-2017-7783?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Q: When was CVE-2017-7783 published?

CVE-2017-7783 was published on 2018-06-11 and last updated on 2026-06-17.

CVE-2017-7783 is a high-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 14% places it in the 96th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 14% (96th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Mozilla Firefox
Published: 2018-06-11
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2017-7783?: 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.
How severe is CVE-2017-7783?: CVE-2017-7783 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2017-7783 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 14% (96th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2017-7783?: CVE-2017-7783 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2017-7783?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2017-7783 published?: CVE-2017-7783 was published on 2018-06-11 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

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