CVE-2015-1555: Zend/Session/SessionManager in Zend Framework 2.2.x before 2.2.9, 2.3.x before 2.3.4 allows remote attackers t

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CRITICAL 9.1REMOTEDOWNGRADE

CVE-2015-1555 is a critical-severity flaw (CVSS 9.1) affecting zend framework. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Zend/Session/SessionManager in Zend Framework 2.2.x before 2.2.9, 2.3.x before 2.3.4 allows remote attackers to create valid sessions without using session validators.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.4% (top 28%)
CISA exploited list	No
Weakness	CWE-20
Published	2017-08-07
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: zend

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2017-08-07 17:29 UTCPublished CVE record published
2026-06-17 00:22 UTCUpdated Record last modified

zend zend framework DOWNGRADE

Affected: 2.2.0 · 2.2.1 · 2.2.2 · 2.2.3 · 2.2.4 · 2.2.5 · 2.2.6 · 2.2.7

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.2.0

1. Check installed version

apt-cache policy zend-framework || rpm -q zend-framework || zend-framework --version

2. No fixed release: DOWNGRADE to a release before 2.2.0 (Debian / Ubuntu)

apt-cache madison zend-framework sudo apt install zend-framework=<VERSION_BEFORE_2.2.0> sudo apt-mark hold zend-framework

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list zend-framework sudo dnf downgrade zend-framework-<VERSION_BEFORE_2.2.0> sudo dnf versionlock add zend-framework

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2015-1555?

zend framework: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2015-1555 being exploited?

CVE-2015-1555 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2015-1555 affect?

CVE-2015-1555 affects zend framework. Severity is critical (CVSS 9.1). Zend/Session/SessionManager in Zend Framework 2.2.x before 2.2.9, 2.3.x before 2.3.4 allows remote attackers to create valid sessions without using session validators.

How urgent is CVE-2015-1555?

Priority 55/100. Critical severity; Remotely exploitable, no login, no user action

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References

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