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Vulnerability details: VCID-g58j-sxrz-p7ee
Vulnerability ID VCID-g58j-sxrz-p7ee
Aliases CVE-2021-31618
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.
Status Published
Exploitability 0.5
Weighted Severity 8.0
Risk 4.0
Affected and Fixed Packages Package Details
Weaknesses (1)
CWE-476 NULL Pointer Dereference
System Score Found at
ssvc Track http://httpd.apache.org/security/vulnerabilities_24.html
cvssv3 7.5 https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-31618.json
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
epss 0.17255 https://api.first.org/data/v1/epss?cve=CVE-2021-31618
cvssv3.1 7.5 https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
apache_httpd important https://httpd.apache.org/security/json/CVE-2021-31618.json
ssvc Track https://lists.apache.org/thread.html/r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E
ssvc Track https://lists.apache.org/thread.html/r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E
ssvc Track https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html
ssvc Track https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/
ssvc Track https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/
cvssv2 5.0 https://nvd.nist.gov/vuln/detail/CVE-2021-31618
cvssv3.1 7.5 https://nvd.nist.gov/vuln/detail/CVE-2021-31618
ssvc Track https://seclists.org/oss-sec/2021/q2/206
archlinux High https://security.archlinux.org/AVG-2041
ssvc Track https://security.gentoo.org/glsa/202107-38
ssvc Track https://security.netapp.com/advisory/ntap-20210727-0008/
ssvc Track https://www.debian.org/security/2021/dsa-4937
ssvc Track https://www.oracle.com/security-alerts/cpuoct2021.html
ssvc Track http://www.openwall.com/lists/oss-security/2021/06/10/9
ssvc Track http://www.openwall.com/lists/oss-security/2024/03/13/2
Reference id Reference type URL
https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-31618.json
https://api.first.org/data/v1/epss?cve=CVE-2021-31618
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-35452
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-26690
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-26691
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-30641
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-31618
https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
https://www.oracle.com/security-alerts/cpuoct2021.html
1968013 https://bugzilla.redhat.com/show_bug.cgi?id=1968013
2 http://www.openwall.com/lists/oss-security/2024/03/13/2
202107-38 https://security.gentoo.org/glsa/202107-38
206 https://seclists.org/oss-sec/2021/q2/206
2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/
9 http://www.openwall.com/lists/oss-security/2021/06/10/9
989562 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989562
A73QJ4HPUMU26I6EULG6SCK67TUEXZYR https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/
ASA-202106-23 https://security.archlinux.org/ASA-202106-23
AVG-2041 https://security.archlinux.org/AVG-2041
cpe:2.3:a:apache:http_server:1.15.17:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:apache:http_server:1.15.17:*:*:*:*:*:*:*
cpe:2.3:a:apache:http_server:2.4.47:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:apache:http_server:2.4.47:*:*:*:*:*:*:*
cpe:2.3:a:oracle:enterprise_manager_ops_center:12.4.0.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:oracle:enterprise_manager_ops_center:12.4.0.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:*:*:*:*:*:*:*
cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
CVE-2021-31618 https://httpd.apache.org/security/json/CVE-2021-31618.json
CVE-2021-31618 https://nvd.nist.gov/vuln/detail/CVE-2021-31618
dsa-4937 https://www.debian.org/security/2021/dsa-4937
msg00006.html https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html
ntap-20210727-0008 https://security.netapp.com/advisory/ntap-20210727-0008/
r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E https://lists.apache.org/thread.html/r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E
r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E https://lists.apache.org/thread.html/r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E
vulnerabilities_24.html http://httpd.apache.org/security/vulnerabilities_24.html
No exploits are available.
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at http://httpd.apache.org/security/vulnerabilities_24.html
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-31618.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://lists.apache.org/thread.html/r14b66ef0f4f569fd515a3f96cd4eb58bd9a8ff525cc326bb0359664f%40%3Ccvs.httpd.apache.org%3E
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://lists.apache.org/thread.html/r783b6558abf3305b17ea462bed4bd66d82866438999bf38cef6d11d1%40%3Ccvs.httpd.apache.org%3E
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/
Vector: AV:N/AC:L/Au:N/C:N/I:N/A:P Found at https://nvd.nist.gov/vuln/detail/CVE-2021-31618
Exploitability (E) Access Vector (AV) Access Complexity (AC) Authentication (Au) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

high

functional

unproven

proof_of_concept

not_defined

local

adjacent_network

network

high

medium

low

multiple

single

none

none

partial

complete

none

partial

complete

none

partial

complete
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://nvd.nist.gov/vuln/detail/CVE-2021-31618
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://seclists.org/oss-sec/2021/q2/206
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://security.gentoo.org/glsa/202107-38
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://security.netapp.com/advisory/ntap-20210727-0008/
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://www.debian.org/security/2021/dsa-4937
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at https://www.oracle.com/security-alerts/cpuoct2021.html
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at http://www.openwall.com/lists/oss-security/2021/06/10/9
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2024-05-20T16:18:33Z/ Found at http://www.openwall.com/lists/oss-security/2024/03/13/2
Exploit Prediction Scoring System (EPSS)
Percentile 0.94751
EPSS Score 0.17255
Published At July 30, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:29:08.774910+00:00 Apache HTTPD Importer Import https://httpd.apache.org/security/json/CVE-2021-31618.json 37.0.0