CVE-2020-8986: lib/NSSDropbox.php in ZendTo prior to 5.22-2 Beta failed to properly check for equality when validating the se

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2020-8986 is a critical-severity flaw (CVSS 9.8) affecting zendto. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

lib/NSSDropbox.php in ZendTo prior to 5.22-2 Beta failed to properly check for equality when validating the session cookie, allowing an attacker to gain administrative access with a large number of requests.

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	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.5% (top 25%)
CISA exploited list	No
Weakness	CWE-754
Published	2020-03-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zend

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

Am I affected?

Timeline

2020-03-24 21:15 UTCPublished CVE record published
2026-06-17 03:27 UTCUpdated Record last modified

zend zendto DOWNGRADE

Affected: 3.10 · 3.11 · 3.12 · 3.13 · 3.20 · 3.51 · 3.52 · 3.53

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.10

1. Check installed version

apt-cache policy zendto || rpm -q zendto || zendto --version

2. No fixed release: DOWNGRADE to a release before 3.10 (Debian / Ubuntu)

apt-cache madison zendto sudo apt install zendto=<VERSION_BEFORE_3.10> sudo apt-mark hold zendto

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

dnf --showduplicates list zendto sudo dnf downgrade zendto-<VERSION_BEFORE_3.10> sudo dnf versionlock add zendto

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-2020-8986?

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

Is CVE-2020-8986 being exploited?

CVE-2020-8986 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-2020-8986 affect?

CVE-2020-8986 affects zendto. Severity is critical (CVSS 9.8). lib/NSSDropbox.php in ZendTo prior to 5.22-2 Beta failed to properly check for equality when validating the session cookie, allowing an attacker to gain administrative access with a large number of requests.

How urgent is CVE-2020-8986?

Priority 58/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

Related CVEs

CVE-2020-8985 HIGH 8.8 DOWNGRADE ZendTo prior to 5.22-2 Beta allowed reflected XSS and CSRF via the unlock.tpl unlock user functionality.
CVE-2020-8984 HIGH 7.5 DOWNGRADE lib/NSSDropbox.php in ZendTo prior to 5.22-2 Beta allowed IP address spoofing via the X-Forwarded-For header.
CVE-2018-1000841 MEDIUM 6.1 UPGRADE Zend.To version Prior to 5.15-1 contains a Cross Site Scripting (XSS) vulnerability in The verify.php page tha

References

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