What’s Vulnerable › Vulnerabilities

CVE-2021-31618: NULL pointer dereference on specially crafted HTTP/2 request

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 51.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-15 · updated 2026-06-17
• Weakness: CWE-476

Description

Apache HTTP Server protocol handler for the HTTP/2 protocol checks received request headers against the size limitations as configured for the server and used for the HTTP/1 protocol as well. On violation of these restrictions and HTTP response is sent to the client with a status code indicating why the request was rejected. This rejection response was not fully initialised in the HTTP/2 protocol handler if the offending header was the very first one received or appeared in a a footer. This led to a NULL pointer dereference on initialised memory, crashing reliably the child process. Since such a triggering HTTP/2 request is easy to craft and submit, this can be exploited to DoS the server. This issue affected mod_http2 1.15.17 and Apache HTTP Server version 2.4.47 only. Apache HTTP Server 2.4.47 was never released.

Affected products

• Apache HTTP Server: 1.15.17, 2.4.47
• Debian Linux: 9.0, 10.0
• Fedoraproject Fedora: 33, 34
• Oracle Corporation Enterprise Manager Ops Center: 12.4.0.0
• Oracle Instantis Enterprisetrack: 17.1, 17.2, 17.3
• Oracle Corporation Oracle ZFS Storage Appliance Kit: 8.8

References

• http://httpd.apache.org/security/vulnerabilities_24.html
• http://www.openwall.com/lists/oss-security/2021/06/10/9
• http://www.openwall.com/lists/oss-security/2024/03/13/2
• https://lists.apache.org/thread.html/r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E
• https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/
• https://seclists.org/oss-sec/2021/q2/206
• https://security.gentoo.org/glsa/202107-38
• https://security.netapp.com/advisory/ntap-20210727-0008/
• https://www.debian.org/security/2021/dsa-4937

Get alerted when CVE-2021-31618 or the next vulnerability affects your stack