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Fencer Intel
high 7.5

CVE-2021-31618 in the critical feed json

NULL pointer dereference on specially crafted HTTP/2 request

published 5y ago modified 2mo ago also BIT-apache-2021-31618 , EUVD-2021-18507

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
52.1%
EPSS 52.1% chance of exploitation in 30 days, percentile 98%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami apache 1.15.18, 2.4.48
  • apache2 Debian 14, Debian 13, Debian 12 2.4.46-5

debian advisories DEBIAN-CVE-2021-31618

  • apache2 SLE Module for Server Applications 15 SP3, SLE Module for Server Applications 15 SP2, SLE Module for Package Hub 15 SP3 +2 more 2.4.43-3.22.1
  • apache2 SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 2.4.23-29.74.1
  • apache2 SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +10 more 2.4.33-3.50.1

suse advisories SUSE-SU-2021:2127-1SUSE-SU-2021:2006-1SUSE-SU-2021:2004-1

  • apache2 openSUSE Leap 15.3 2.4.43-3.22.1
  • apache2 openSUSE Leap 15.2 2.4.43-lp152.2.15.1

opensuse advisories openSUSE-SU-2021:2127-1openSUSE-SU-2021:0908-1

  • apache2 Alpine 3.24, Alpine 3.23, Alpine 3.22 +12 more 2.4.48-r0

alpine advisories ALPINE-CVE-2021-31618

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • mod_http2 Azure Linux 3.0 2.0.29-3

azure linux advisories AZL-44166

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • apache Arch Linux 2.4.48-1

arch linux advisories AVG-2041

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-31618 updated cvss 7.5

httpd: NULL pointer dereference on specially crafted HTTP/2 request

  • Red Hat Enterprise Linux 6 httpd, mod_ssl, httpd-tools, httpd-manual Red Hat Enterprise Linux 7 httpd, mod_ssl, mod_ldap, httpd-tools, mod_session, httpd-manual, +1 more Red Hat Enterprise Linux 8 httpd, mod_md, mod_ssl, mod_ldap, mod_http2, httpd-tools, +4 more Red Hat Enterprise Linux 9 httpd, mod_lua, mod_ssl, mod_ldap, httpd-core, httpd-tools, +4 more Red Hat JBoss Core Services jbcs-httpd24-httpd Red Hat JBoss Enterprise Application Platform 6 httpd22 httpd22
    +2 more products
    Red Hat JBoss Enterprise Web Server 2 httpd22 httpd22 Red Hat Software Collections httpd24-httpd, httpd24-mod_md, httpd24-mod_ssl, httpd24-mod_ldap, httpd24-httpd-tools, httpd24-mod_session, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2y ago

Exploit prediction

52.14% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
bitnami apache
>=1.15.17, <1.15.18
>=2.4.47, <2.4.48
1.15.18
2.4.48

Affected products

  • Apache Software Foundation Apache HTTP Server

Classification

Weakness
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.