CVE-2021-26691: Apache HTTP Server

Critical severity, CVSS 9.8. EPSS: 68.3% chance of exploitation in the next 30 days.

In Apache HTTP Server versions 2.4.0 to 2.4.46 a specially crafted SessionHeader sent by an origin server could cause a heap overflow

Affected products

• Apache HTTP Server: from 2.4.0, up to and including 2.4.46
• Debian Debian Linux: version 9.0 only; version 10.0 only
• Fedoraproject Fedora: version 34 only; version 35 only
• Netapp Cloud Backup: affected versions not specified
• Oracle Enterprise Manager Ops Center: version 12.4.0.0 only
• Oracle Instantis Enterprisetrack: version 17.1 only; version 17.2 only; version 17.3 only
• Oracle Secure Backup: before 18.1.0.1.0 (fixed in 18.1.0.1.0)
• Oracle ZFS Storage Appliance Kit: version 8.8 only

Published 2021-06-10. Last modified 2026-06-17.