CVE-2026-40021

Exploitation

Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.

SSVC decision

• ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
• AutomatablenoAt least one step from reconnaissance to exploitation cannot be reliably automated.
• Technical ImpactpartialSuccessful exploitation gives limited control of the vulnerable component.

CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.

EPSS probability

0.77% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 55.4% of scored records. A rank, not a probability.

NVD base score

6.3 (CVSS v4.0), scored by the NVD independently of the CNA.

NVD CVSS vector

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

NVD analysis status

Analyzed. NVD last modified this record on 2026-10-26.

Red Hat severity

No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2026-04-10 15:44Z6 MO AGO

Last updated

2026-04-10 17:35Z6 MO AGO

Reserved

2026-04-08

Assigning CNA

apache

Record state

PUBLISHED

Severity

Medium (CVSS 6.3)

CNA CVSS vector

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Weaknesses

• CWE-116Improper Encoding or Escaping of OutputClass

Data version

5.2

Document digest

716815ee01cf1e0459b635273d6e34cc0c2c5fa58d19bb59b471a2ac2f0fdf6f

• github.comhttps://github.com/apache/logging-log4net/pull/280patch
• logging.apache.orghttps://logging.apache.org/security.html#CVE-2026-40021vendor-advisory
• logging.apache.orghttps://logging.apache.org/cyclonedx/vdr.xmlvendor-advisory
• logging.apache.orghttps://logging.apache.org/log4net/manual/configuration/layouts.htmlrelated
• lists.apache.orghttps://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7vendor-advisory
• www.openwall.comhttp://www.openwall.com/lists/oss-security/2026/04/10/11