CVE-2021-31618
HighApache 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.
Published Jul 12, 2021 · Updated Sep 23, 2026 · Also known as ALPINE-CVE-2021-31618, BIT-apache-2021-31618, DEBIAN-CVE-2021-31618
Key Facts
Patch immediately- CVE-2021-31618 is a high-severity vulnerability (CVSS 7.5 v3.1) affecting HTTP Server (Apache), Enterprise Manager Ops Center (Oracle), Instantis Enterprisetrack (Oracle) and 22 more products.
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 51% probability of exploitation in the next 30 days.
- Fixed versions are available, including apache 1.15.18, apache 2.4.48, apache 2.4.48-1.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (30-day exploit likelihood)
51%
Higher than 98.9% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
Get the full CVE-2021-31618 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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
274 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| HTTP ServerApache | 1.15.17, 2.4.47, >= 2.4.47 | n/a |
| Enterprise Manager Ops CenterOracle | 12.4.0.0 | n/a |
| Instantis EnterprisetrackOracle | 17.1, 17.2, 17.3 | n/a |
| Zfs Storage Appliance KitOracle | 8.8 | n/a |
| Debian LinuxDebian | 10.0, 9.0 | n/a |
Patched Releases
apache
1.15.18, 2.4.48, 2.4.48-1
apache2
2.4.23-29.74.1, 2.4.25-3+deb9u10, 2.4.33-3.50.1, 2.4.38-3+deb10u5, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1, 2.4.46-5, 2.4.48-r0
apache2-devel
2.4.23-29.74.1, 2.4.33-3.50.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-doc
2.4.23-29.74.1, 2.4.33-3.50.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-event
2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-example-pages
2.4.23-29.74.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-prefork
2.4.23-29.74.1, 2.4.33-3.50.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-utils
2.4.23-29.74.1, 2.4.33-3.50.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
apache2-worker
2.4.23-29.74.1, 2.4.33-3.50.1, 2.4.43-3.22.1, 2.4.43-lp152.2.15.1
httpd
2.4.46-2.amzn2
httpd-devel
2.4.46-2.amzn2
httpd-filesystem
2.4.46-2.amzn2
httpd-manual
2.4.46-2.amzn2
httpd-tools
2.4.46-2.amzn2
mod_http2
1.15.19-1.amzn2.0.1, 2.0.29-3
mod_ldap
2.4.46-2.amzn2
mod_md
2.4.46-2.amzn2
mod_proxy_html
1:2.4.46-2.amzn2
mod_session
2.4.46-2.amzn2
mod_ssl
1:2.4.46-2.amzn2
rootio-apache2
2.4.46-5
Timeline
Publicly disclosed
Jul 12, 2021
Last updated
Sep 23, 2026
Weakness Type
- CWE-476 NULL Pointer Dereference
References
- advisoryhttp://httpd.apache.org/security/vulnerabilities_24.html
- advisoryhttps://bugzilla.suse.com/1145740
- advisoryhttps://bugzilla.suse.com/1180530
- advisoryhttps://bugzilla.suse.com/1182703
- advisoryhttps://bugzilla.suse.com/1186922
FAQ
Common Questions.
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.
Affected: HTTP Server (Apache) versions 1.15.17, 2.4.47, >= 2.4.47; Enterprise Manager Ops Center (Oracle) versions 12.4.0.0; Instantis Enterprisetrack (Oracle) versions 17.1, 17.2, 17.3, among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including apache 1.15.18, apache 2.4.48, apache 2.4.48-1.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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