How severe is CVE-2021-40540?

CVE-2021-40540 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-40540 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40540?

CVE-2021-40540 affects Ulfius Project Ulfius. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40540?

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

When was CVE-2021-40540 published?

CVE-2021-40540 was published on 2021-09-07 and last updated on 2026-06-17.

CVE-2021-40540

CVE-2021-40540 is a critical-severity vulnerability in Ulfius Project Ulfius with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (84th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Ulfius Project Ulfius
Published: 2021-09-07
Last modified: 2026-06-17

Description

ulfius_uri_logger in Ulfius HTTP Framework before 2.7.4 omits con_info initialization and a con_info->request NULL check for certain malformed HTTP requests.

Frequently asked questions

What is CVE-2021-40540?: ulfius_uri_logger in Ulfius HTTP Framework before 2.7.4 omits con_info initialization and a con_info->request NULL check for certain malformed HTTP requests.
How severe is CVE-2021-40540?: CVE-2021-40540 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40540 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40540?: CVE-2021-40540 affects Ulfius Project Ulfius. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40540?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-40540 published?: CVE-2021-40540 was published on 2021-09-07 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:ulfius_project:ulfius:*:*:*:*:*:*:*:*