How severe is CVE-2019-12831?

CVE-2019-12831 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2019-12831 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2019-12831?

CVE-2019-12831 affects Mybb. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2019-12831?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2019-12831 published?

CVE-2019-12831 was published on 2019-06-15 and last updated on 2026-06-17.

CVE-2019-12831

CVE-2019-12831 is a high-severity vulnerability in Mybb with a CVSS 3.x base score of 7.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.2)
CVSS v2: 6.5
EPSS exploit prediction: 1% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Mybb
Published: 2019-06-15
Last modified: 2026-06-17

Description

In MyBB before 1.8.21, an attacker can abuse a default behavior of MySQL on many systems (that leads to truncation of strings that are too long for a database column) to create a PHP shell in the cache directory of a targeted forum via a crafted XML import, as demonstrated by truncation of aaaaaaaaaaaaaaaaaaaaaaaaaa.php.css to aaaaaaaaaaaaaaaaaaaaaaaaaa.php with a 30-character limit, aka theme import stylesheet name RCE.

Frequently asked questions

What is CVE-2019-12831?: In MyBB before 1.8.21, an attacker can abuse a default behavior of MySQL on many systems (that leads to truncation of strings that are too long for a database column) to create a PHP shell in the cache directory of a targeted forum via a crafted XML import, as demonstrated by truncation of aaaaaaaaaaaaaaaaaaaaaaaaaa.php.css to aaaaaaaaaaaaaaaaaaaaaaaaaa.php with a 30-character limit, aka theme import stylesheet name RCE.
How severe is CVE-2019-12831?: CVE-2019-12831 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2019-12831 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2019-12831?: CVE-2019-12831 affects Mybb. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2019-12831?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2019-12831 published?: CVE-2019-12831 was published on 2019-06-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:mybb:mybb:*:*:*:*:*:*:*:*

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