No exploitation reported

CVE-2016-4423

No exploitation reported by the sources we read.

Published2016-06-01
WeaknessCWE-399

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2016-06-0122:59CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2016-4423?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2016-4423?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Symfony

Branch	Affected	Fixed in	Source
2.3	≤ 2.3.40	no fix published	NVD
2.7	= 2.7.0	no fix published	NVD
2.7	= 2.7.1	no fix published	NVD
2.7	= 2.7.2	no fix published	NVD
2.7	= 2.7.3	no fix published	NVD
2.7	= 2.7.4	no fix published	NVD
2.7	= 2.7.5	no fix published	NVD
2.7	= 2.7.6	no fix published	NVD
2.7	= 2.7.7	no fix published	NVD
2.7	= 2.7.8	no fix published	NVD
2.7	= 2.7.9	no fix published	NVD
2.7	= 2.7.10	no fix published	NVD

Debian debian linux

Branch	Affected	Fixed in	Source
8.0	= 8.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

symfony.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.07.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
NVDweakness (CWE)CWE-399read 2026-10-23
FIRST EPSSEPSS score1.9 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2016-06-01
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2016-4423?

Is CVE-2016-4423 actively exploited?

Active exploitation of CVE-2016-4423 has not been confirmed. Its EPSS score was 1.9% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

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

CVE-2016-4423 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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