CVE-2021-31618

NULL pointer dereference on specially crafted HTTP/2 request

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.

Remediation

Workaround:

  • On unpatched servers, the `h2` protocol can be disabled by removing it from the `Protocols` configuration. If the `h2` protocol is not enabled, the server is not affected by this vulnerability.

Category

7.5
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 18.52% Top 10%
Vendor Advisory fedoraproject.org Vendor Advisory fedoraproject.org Vendor Advisory debian.org Vendor Advisory gentoo.org Vendor Advisory apache.org
Affected: Apache Software Foundation Apache HTTP Server
Published at:
Updated at:

References

Link Tags
http://httpd.apache.org/security/vulnerabilities_24.html release notes vendor advisory
http://www.openwall.com/lists/oss-security/2021/06/10/9 third party advisory mailing list
https://seclists.org/oss-sec/2021/q2/206 third party advisory mailing list
https://lists.apache.org/thread.html/r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E mailing list
https://lists.apache.org/thread.html/r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E mailing list
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/ vendor advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/ vendor advisory
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html third party advisory mailing list
https://www.debian.org/security/2021/dsa-4937 third party advisory vendor advisory
https://security.gentoo.org/glsa/202107-38 third party advisory vendor advisory
https://www.oracle.com/security-alerts/cpuoct2021.html third party advisory patch
https://security.netapp.com/advisory/ntap-20210727-0008/ third party advisory
http://www.openwall.com/lists/oss-security/2024/03/13/2 mailing list

Frequently Asked Questions

What is the severity of CVE-2021-31618?
CVE-2021-31618 has been scored as a high severity vulnerability.
How to fix CVE-2021-31618?
As a workaround for remediating CVE-2021-31618: On unpatched servers, the `h2` protocol can be disabled by removing it from the `Protocols` configuration. If the `h2` protocol is not enabled, the server is not affected by this vulnerability.
Is CVE-2021-31618 being actively exploited in the wild?
It is possible that CVE-2021-31618 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~19% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-31618?
CVE-2021-31618 affects Apache Software Foundation Apache HTTP Server.
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