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
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Apache Software Foundation | Apache HTTP Server | 2.4.47 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | apache2 | 2.4.46-5 | — |
| Debian 13 | apache2 | 2.4.46-5 | — |
| Debian 12 | apache2 | 2.4.46-5 | — |
| Debian 10 | apache2 | 2.4.38-3+deb10u5 | DSA-4937-1 |
| Debian 9 | apache2 | 2.4.25-3+deb9u10 | DLA-2706-1 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP3 | apache2 | 2.4.43-3.22.1 | SUSE-SU-2021:2127-1 |
| SLES 15 SP2 | apache2 | 2.4.43-3.22.1 | SUSE-SU-2021:2127-1 |
| SLES 15 SP1 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SLES 15 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SLES 12 SP5 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
Show 19 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 12 SP4 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLES 12 SP3 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLES 12 SP2 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLES for SAP 15 SP1 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SLES for SAP 15 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SLES for SAP 12 SP5 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLES for SAP 12 SP4 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLES for SAP 12 SP3 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SLE HPC 15 SP1 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SLE HPC 15 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SUSE OpenStack Cloud Crowbar 9 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SUSE OpenStack Cloud Crowbar 8 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SUSE OpenStack Cloud 9 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SUSE OpenStack Cloud 8 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SUSE Manager Server 4.0 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SUSE Manager Retail Branch Server 4.0 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SUSE Manager Proxy 4.0 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
| SUSE HPE Helion OpenStack 8 | apache2 | 2.4.23-29.74.1 | SUSE-SU-2021:2006-1 |
| SUSE Enterprise Storage 6 | apache2 | 2.4.33-3.50.1 | SUSE-SU-2021:2004-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Leap 15.3 | apache2 | 2.4.43-3.22.1 | openSUSE-SU-2021:2127-1 |
| openSUSE Leap 15.2 | apache2 | 2.4.43-lp152.2.15.1 | openSUSE-SU-2021:0908-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | apache2 | 2.4.48-r0 | — |
| Alpine v3.23 | apache2 | 2.4.48-r0 | — |
| Alpine v3.22 | apache2 | 2.4.48-r0 | — |
| Alpine v3.21 | apache2 | 2.4.48-r0 | — |
| Alpine v3.20 | apache2 | 2.4.48-r0 | — |
Show 10 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | apache2 | 2.4.48-r0 | — |
| Alpine v3.18 | apache2 | 2.4.48-r0 | — |
| Alpine v3.17 | apache2 | 2.4.48-r0 | — |
| Alpine v3.16 | apache2 | 2.4.48-r0 | — |
| Alpine v3.15 | apache2 | 2.4.48-r0 | — |
| Alpine v3.14 | apache2 | 2.4.48-r0 | — |
| Alpine v3.13 | apache2 | 2.4.48-r0 | — |
| Alpine v3.12 | apache2 | 2.4.48-r0 | — |
| Alpine v3.11 | apache2 | 2.4.48-r0 | — |
| Alpine v3.10 | apache2 | 2.4.48-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2 | httpd +7 | 2.4.46-2.amzn2 | ALAS2-2021-1672 |
| Amazon Linux 2 | mod_http2 | 1.15.19-1.amzn2.0.1 | ALAS2-2021-1678 |
| Amazon Linux 2 | mod_ssl +1 | 1:2.4.46-2.amzn2 | ALAS2-2021-1672 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | mod_http2 | 2.0.29-3 | — |
Advisories 10
- DSA-4937-1 apache2 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2706-1 apache2 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- SUSE-SU-2021:2004-1 Security update for apache2 SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:0908-1 Security update for apache2 SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:2127-1 Security update for apache2 SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:2127-1 Security update for apache2 SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:2006-1 Security update for apache2 SUSE / openSUSE Security Updates · Feb 4, 2026
- WID-SEC-2024-1591 Juniper JUNOS: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 11, 2024
- ALAS2-2021-1678 Important: mod_http2 security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Jul 1, 2021
- ALAS2-2021-1672 Important: httpd security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Jun 24, 2021
References
- http://httpd.apache.org/security/vulnerabilities_24.html
- [oss-security] 20210609 CVE-2021-31618: Apache httpd: NULL pointer dereference on specially crafted HTTP/2 request mailing-list
- https://seclists.org/oss-sec/2021/q2/206
- [httpd-cvs] 20210615 svn commit: r1890801 - /httpd/site/trunk/content/security/json/CVE-2021-31618.json mailing-list
- [httpd-cvs] 20210615 svn commit: r1075782 - in /websites/staging/httpd/trunk/content: ./ security/json/CVE-2021-31618.json security/vulnerabilities_24.html mailing-list
- FEDORA-2021-051639aad4 vendor-advisory
- FEDORA-2021-181f29c392 vendor-advisory
- [debian-lts-announce] 20210709 [SECURITY] [DLA 2706-1] apache2 security update mailing-list
- DSA-4937 vendor-advisory
- GLSA-202107-38 vendor-advisory
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://security.netapp.com/advisory/ntap-20210727-0008/
- [oss-security] 20240313 Re: CVE-2021-31618: Apache httpd: NULL pointer dereference on specially crafted HTTP/2 request mailing-list