How severe is CVE-2021-28040?

CVE-2021-28040 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-28040 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-28040?

CVE-2021-28040 affects Ossec. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-28040?

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-2021-28040 published?

CVE-2021-28040 was published on 2021-03-05 and last updated on 2026-06-17.

CVE-2021-28040

CVE-2021-28040 is a high-severity vulnerability in Ossec with a CVSS 3.x base score of 7.5. 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-674.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (64th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-674
Affected product: Ossec
Published: 2021-03-05
Last modified: 2026-06-17

Description

An issue was discovered in OSSEC 3.6.0. An uncontrolled recursion vulnerability in os_xml.c occurs when a large number of opening and closing XML tags is used. Because recursion is used in _ReadElem without restriction, an attacker can trigger a segmentation fault once unmapped memory is reached.

Frequently asked questions

What is CVE-2021-28040?: An issue was discovered in OSSEC 3.6.0. An uncontrolled recursion vulnerability in os_xml.c occurs when a large number of opening and closing XML tags is used. Because recursion is used in _ReadElem without restriction, an attacker can trigger a segmentation fault once unmapped memory is reached.
How severe is CVE-2021-28040?: CVE-2021-28040 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-28040 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-28040?: CVE-2021-28040 affects Ossec. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-28040?: 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-2021-28040 published?: CVE-2021-28040 was published on 2021-03-05 and last updated on 2026-06-17.

References

https://github.com/ossec/ossec-hids/issues/1953

Affected products (1)

cpe:2.3:a:ossec:ossec:3.6.0:*:*:*:*:*:*:*

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