CVE-2021-40540: ulfius_uri_logger in Ulfius HTTP Framework before 2.7.4 omits con_info initialization and a con_info->request

Q: How do I fix CVE-2021-40540?

ulfius: upgrade to 2.7.4. Exact commands for each OS are on this page.

Q: Is CVE-2021-40540 being exploited?

CVE-2021-40540 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-40540 affect?

CVE-2021-40540 affects ulfius. Severity is critical (CVSS 9.8). 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.

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-40540 is a critical-severity flaw (CVSS 9.8) affecting ulfius. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Public exploit reference
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	2.6% (top 15%)
CISA exploited list	No
Published	2021-09-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: ulfius project

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

Am I affected?

Timeline

2021-09-07 02:15 UTCPublished CVE record published
2026-06-17 04:07 UTCUpdated Record last modified

ulfius project ulfius UPGRADE

Affected: < 2.7.4

Fixed in: 2.7.4

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2.7.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ulfius

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ulfius

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2021-40540?

ulfius: upgrade to 2.7.4. Exact commands for each OS are on this page.

Is CVE-2021-40540 being exploited?

CVE-2021-40540 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-2021-40540 affect?

CVE-2021-40540 affects ulfius. Severity is critical (CVSS 9.8). 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 urgent is CVE-2021-40540?

Priority 66/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

← Back to latest CVEs