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CVE-2016-4423

Symphony Denial of Service Via Overlong Usernames

7.5 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

1.86%Up 0.7 points since Feb 4, 2022
90%50%10%1%

What each source reports

NVD Score used 7.5

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.

Record
CVE-2016-4423
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-399
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2016-4423
Updated
2026-11-02
EUVDEUVD-2022-5580 No score

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.

Record
EUVD-2022-5580
Updated
2026-11-03
GitHub AdvisoriesGHSA-whgv-8cg3-7hcm 7.5

Symphony Denial of Service Via Overlong Usernames

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.

Record
GHSA-whgv-8cg3-7hcm
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSV 7.5

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.

Record
CVE-2016-4423
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2016-4423 7.5

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.

Record
DEBIAN-CVE-2016-4423
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVGHSA-whgv-8cg3-7hcm 7.5

Symphony Denial of Service Via Overlong Usernames

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.

Record
GHSA-whgv-8cg3-7hcm
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2016-4423 7.5

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.

Record
UBUNTU-CVE-2016-4423
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
symfony/security-http
Packagist
 2.3.0 up to 2.3.41
2.3.41
symfony/security-http
Packagist
 2.4.0 up to 2.7.13
2.7.13
symfony/security-http
Packagist
 2.8.0 up to 2.8.6
2.8.6
symfony/security-http
Packagist
 3.0.0 up to 3.0.6
3.0.6
symfony/security
Packagist
 2.3.0 up to 2.3.41
2.3.41
symfony/security
Packagist
 2.4.0 up to 2.7.13
2.7.13
symfony/security
Packagist
 2.8.0 up to 2.8.6
2.8.6
symfony/security
Packagist
 3.0.0 up to 3.0.6
3.0.6
symfony/symfony
Packagist
 2.3.0 up to 2.3.41
2.3.41
symfony/symfony
Packagist
 2.4.0 up to 2.7.13
2.7.13
Show 18 moreShow less
Affected packages
PackageAffectedFixed
symfony/symfony
Packagist
 2.8.0 up to 2.8.6
2.8.6
symfony/symfony
Packagist
 3.0.0 up to 3.0.6
3.0.6
symfony
Debian:12
 before 2.8.6+dfsg-1
2.8.6+dfsg-1
symfony
Debian:13
 before 2.8.6+dfsg-1
2.8.6+dfsg-1
symfony
Debian:14
 before 2.8.6+dfsg-1
2.8.6+dfsg-1
symfony
Debian:8
 before 2.3.21+dfsg-4+deb8u3, plus listed versions
2.3.21+dfsg-42.3.21+dfsg-4+deb8u12.3.21+dfsg-4+deb8u2
2.3.21+dfsg-4+deb8u3
symfony/security-http
Packagist
 2.4.0 up to 2.7.13, plus listed versions
v2.4.0v2.4.1v2.4.10v2.4.2v2.4.3
Show 45 moreShow less
v2.4.4v2.4.5v2.4.6v2.4.7v2.4.8v2.4.9v2.5.0v2.5.0-BETA1v2.5.0-BETA2v2.5.0-RC1v2.5.1v2.5.10v2.5.11v2.5.12v2.5.2v2.5.3v2.5.4v2.5.5v2.5.6v2.5.7v2.5.8v2.5.9v2.6.0v2.6.0-BETA1v2.6.0-BETA2v2.6.1v2.6.10v2.6.11v2.6.12v2.6.13v2.6.2v2.6.3v2.6.4v2.6.5v2.6.6v2.6.7v2.6.8v2.6.9v2.7.0v2.7.0-BETA1v2.7.0-BETA2v2.7.1v2.7.10v2.7.11v2.7.12
2.7.13
symfony/security-http
Packagist
 2.8.0 up to 2.8.6, plus listed versions
v2.8.0v2.8.1v2.8.2v2.8.3v2.8.4v2.8.5
2.8.6
symfony/security-http
Packagist
 3.0.0 up to 3.0.6, plus listed versions
v3.0.0v3.0.1v3.0.2v3.0.3v3.0.4v3.0.5
3.0.6
symfony/security
Packagist
 2.3.0 up to 2.3.41, plus listed versions
v2.3.0v2.3.1v2.3.10v2.3.11v2.3.12
Show 36 moreShow less
v2.3.13v2.3.14v2.3.15v2.3.16v2.3.17v2.3.18v2.3.19v2.3.2v2.3.20v2.3.21v2.3.22v2.3.23v2.3.24v2.3.25v2.3.26v2.3.27v2.3.28v2.3.29v2.3.3v2.3.30v2.3.31v2.3.32v2.3.33v2.3.34v2.3.35v2.3.36v2.3.37v2.3.38v2.3.39v2.3.4v2.3.40v2.3.5v2.3.6v2.3.7v2.3.8v2.3.9
2.3.41
symfony/security
Packagist
 2.4.0 up to 2.7.13, plus listed versions
v2.4.0v2.4.1v2.4.10v2.4.2v2.4.3
Show 45 moreShow less
v2.4.4v2.4.5v2.4.6v2.4.7v2.4.8v2.4.9v2.5.0v2.5.0-BETA1v2.5.0-BETA2v2.5.0-RC1v2.5.1v2.5.10v2.5.11v2.5.12v2.5.2v2.5.3v2.5.4v2.5.5v2.5.6v2.5.7v2.5.8v2.5.9v2.6.0v2.6.0-BETA1v2.6.0-BETA2v2.6.1v2.6.10v2.6.11v2.6.12v2.6.13v2.6.2v2.6.3v2.6.4v2.6.5v2.6.6v2.6.7v2.6.8v2.6.9v2.7.0v2.7.0-BETA1v2.7.0-BETA2v2.7.1v2.7.10v2.7.11v2.7.12
2.7.13
symfony/security
Packagist
 2.8.0 up to 2.8.6, plus listed versions
v2.8.0v2.8.1v2.8.2v2.8.3v2.8.4v2.8.5
2.8.6
symfony/security
Packagist
 3.0.0 up to 3.0.6, plus listed versions
v3.0.0v3.0.1v3.0.2v3.0.3v3.0.4v3.0.5
3.0.6
symfony/symfony
Packagist
 2.3.0 up to 2.3.41, plus listed versions
v2.3.0v2.3.1v2.3.10v2.3.11v2.3.12
Show 36 moreShow less
v2.3.13v2.3.14v2.3.15v2.3.16v2.3.17v2.3.18v2.3.19v2.3.2v2.3.20v2.3.21v2.3.22v2.3.23v2.3.24v2.3.25v2.3.26v2.3.27v2.3.28v2.3.29v2.3.3v2.3.30v2.3.31v2.3.32v2.3.33v2.3.34v2.3.35v2.3.36v2.3.37v2.3.38v2.3.39v2.3.4v2.3.40v2.3.5v2.3.6v2.3.7v2.3.8v2.3.9
2.3.41
symfony/symfony
Packagist
 2.4.0 up to 2.7.13, plus listed versions
v2.4.0v2.4.1v2.4.10v2.4.2v2.4.3
Show 45 moreShow less
v2.4.4v2.4.5v2.4.6v2.4.7v2.4.8v2.4.9v2.5.0v2.5.0-BETA1v2.5.0-BETA2v2.5.0-RC1v2.5.1v2.5.10v2.5.11v2.5.12v2.5.2v2.5.3v2.5.4v2.5.5v2.5.6v2.5.7v2.5.8v2.5.9v2.6.0v2.6.0-BETA1v2.6.0-BETA2v2.6.1v2.6.10v2.6.11v2.6.12v2.6.13v2.6.2v2.6.3v2.6.4v2.6.5v2.6.6v2.6.7v2.6.8v2.6.9v2.7.0v2.7.0-BETA1v2.7.0-BETA2v2.7.1v2.7.10v2.7.11v2.7.12
2.7.13
symfony/symfony
Packagist
 2.8.0 up to 2.8.6, plus listed versions
v2.8.0v2.8.1v2.8.2v2.8.3v2.8.4v2.8.5
2.8.6
symfony/symfony
Packagist
 3.0.0 up to 3.0.6, plus listed versions
v3.0.0v3.0.1v3.0.2v3.0.3v3.0.4v3.0.5
3.0.6
symfony
Ubuntu:16.04:LTS
 All versions, plus listed versions
2.7.1+dfsg-12.7.5+dfsg-12.7.9+dfsg-12.7.9+dfsg-1ubuntu22.7.10-0ubuntu2
 None known

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2016-4423 is a high vulnerability (CVSS 7.5) in Sensiolabs Symfony, published May 29, 2016. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.86%, the 79th percentile. Fixed in symfony/security-http 2.3.41.

References

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Left out here: 24 versions. The JSON record has them.

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