CVE-2011-10018: myBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2011-10018 is a critical-severity flaw (CVSS 9.8) affecting mybb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

myBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code. The backdoor allowed remote attackers to execute arbitrary PHP code by injecting payloads into a specially crafted collapsed cookie. This vulnerability was introduced during packaging and was not part of the intended application logic. Exploitation requires no authentication and results in full compromise of the web server under the context of the web ap

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.9% (top 13%)
CISA exploited list	No
Weakness	CWE-94, CWE-912
Published	2025-08-13
Last modified	2026-06-16

Publisher (CNA): VulnCheck · Vendor: mybb

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-08-13 21:15 UTCPublished CVE record published
2026-06-16 23:28 UTCUpdated Record last modified

mybb mybb DOWNGRADE

Affected: 1.6.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.6.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.6.4 (Debian / Ubuntu)

apt-cache madison mybb sudo apt install mybb=<VERSION_BEFORE_1.6.4> sudo apt-mark hold mybb

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

dnf --showduplicates list mybb sudo dnf downgrade mybb-<VERSION_BEFORE_1.6.4> sudo dnf versionlock add mybb

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · R · FIXED · 4.6.2-1.fc46 · FEDORA-2026-1dd919a262 · source

sudo dnf upgrade --advisory=FEDORA-2026-1dd919a262

Fedora ELN · perl-Mail-AuthenticationResults · FIXED · 2.20261029-1.eln159 · FEDORA-2026-a2c11d7da6 · source

sudo dnf upgrade --advisory=FEDORA-2026-a2c11d7da6

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: web.archive.org/web/20111015224948/http://secunia.com/advisories/46300/
Write-up: www.exploit-db.com/exploits/17949
Write-up: www.vulncheck.com/advisories/mybb-backdoor-arbitrary-command-execution
Metasploit: myBB 1.6.4 Backdoor Arbitrary Command Execution

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-2011-10018?

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

Is CVE-2011-10018 being exploited?

CVE-2011-10018 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-2011-10018 affect?

CVE-2011-10018 affects mybb. Severity is critical (CVSS 9.8). myBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code. The backdoor allowed remote attackers to execute arbitrary PHP code by injecting payloads into a specially crafted collapsed cookie. This vulnerab

How urgent is CVE-2011-10018?

Priority 69/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

Related CVEs

CVE-2025-48941 MEDIUM 5.3 UPGRADE MyBB is free and open source forum software
CVE-2025-48940 HIGH 7.2 UPGRADE MyBB is free and open source forum software
CVE-2025-29460 HIGH 7.6 DOWNGRADE An issue in MyBB 1.8.38 allows a remote attacker to obtain sensitive information via the Add Mycode function
CVE-2025-29459 HIGH 7.6 DOWNGRADE An issue in MyBB 1.8.38 allows a remote attacker to obtain sensitive information via the Mail function
CVE-2025-29458 HIGH 7.6 DOWNGRADE An issue in MyBB 1.8.38 allows a remote attacker to obtain sensitive information via the Change Avatar functio

References

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