CVE-2023-53977: myBB Forums 1.8.26 contains a stored cross-site scripting vulnerability in the forum management system that al

Routine

MEDIUM 5.4DOWNGRADE

CVE-2023-53977 is a medium-severity flaw (CVSS 5.4) affecting mybb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

myBB Forums 1.8.26 contains a stored cross-site scripting vulnerability in the forum management system that allows authenticated administrators to inject malicious scripts when creating new forums. Attackers can exploit this vulnerability by inserting script payloads in the forum title field when adding new forums through the 'Forums and Posts' > 'Forum Management' interface, causing arbitrary JavaScript to execute when the forum listing is viewe

Why this priority

Public exploit reference

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

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-79
Published	2025-12-22
Last modified	2026-06-17

Publisher (CNA): VulnCheck · Vendor: mybb

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

Am I affected?

Timeline

2025-12-22 22:16 UTCPublished CVE record published
2026-06-17 06:46 UTCUpdated Record last modified

mybb mybb DOWNGRADE

Affected: 1.8.26

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.8.26

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.8.26 (Debian / Ubuntu)

apt-cache madison mybb sudo apt install mybb=<VERSION_BEFORE_1.8.26> sudo apt-mark hold mybb

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

dnf --showduplicates list mybb sudo dnf downgrade mybb-<VERSION_BEFORE_1.8.26> 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.

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-2023-53977?

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

Is CVE-2023-53977 being exploited?

CVE-2023-53977 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-2023-53977 affect?

CVE-2023-53977 affects mybb. Severity is medium (CVSS 5.4). myBB Forums 1.8.26 contains a stored cross-site scripting vulnerability in the forum management system that allows authenticated administrators to inject malicious scripts when creating new forums. Attackers can exploit this vulnerability b

How urgent is CVE-2023-53977?

Priority 28/100. Public exploit reference

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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