Is CVE-2016-4423 in the CISA KEV catalog?

No. CVE-2016-4423 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2016-4423?

CVE-2016-4423 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2016-4423?

CVE-2016-4423 has an EPSS score of 1.86% (77th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2016-4423?

Upgrade symfony on debian 11 to 2.8.6+dfsg-1 or later.

CVE & CISA-KEV Catalog

CVE-2016-4423

HIGHEPSS 77th pctl

7.5

CVSS v3

NVD

Description

The attemptAuthentication function in Component/Security/Http/Firewall/UsernamePasswordFormAuthenticationListener.php in Symfony before 2.3.41, 2.7.x before 2.7.13, 2.8.x before 2.8.6, and 3.0.x before 3.0.6 does not limit the length of a username stored in a session, which allows remote attackers to cause a denial of service (session storage consumption) via a series of authentication attempts with long, non-existent usernames.

CWE-399Resource Management Errors

How to fix

Remediation Available

symfonyDebian

Fixed in:2.8.6+dfsg-1CVE-2016-4423

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

1.86%probability of exploitation in 30 days

77thpercentile

Elevated risk: more likely to be exploited than 77% of all known CVEs.

References

Vendor Advisory1

symfony.com

Other references2

Related Vulnerabilities

Other CWE-399 (Resource Management Errors) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2009-3103	High	10.0	90%	-	-
CVE-2009-0075	High	9.3	85%	-	-
CVE-2005-1790	Low	2.6	83%	-	-
CVE-2010-0806	High	8.8	82%	KEV	-
CVE-2009-2526	High	7.8	82%	-	-
CVE-2015-1868	High	7.8	82%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-06.