CVE-2021-31618: NULL pointer dereference on specially crafted HTTP/2 request
Vulnerability summary
CVE-2021-31618 is a high (CVSS 7.5) NULL Pointer Dereference vulnerability in apache software foundation apache http server. EPSS estimates a 51.49% chance of exploitation in the next 30 days, higher than 98.9% of scored vulnerabilities.
Severe, CVSS 7.5 (NVD); no exploitation reported by the 5 checked sources; EPSS 51% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 8 · Related 5Timeline
- 15-06-2021PublishedVulnerability first disclosed.
- 03-08-2024Last modifiedVulnerability information updated.
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.
CVSS metrics
4 scores · 3 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
51.49%
Chance of exploitation in the next 30 days
Percentile
99%
Versus all other CVEs
30-day change
No change 0.00 pp
From 51.49% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Oracle3 products
- enterprise_manager_ops_center12.4.0.0
- instantis_enterprisetrack17.1 | 17.2 | 17.3
- zfs_storage_appliance_kit8.8
Debian2 products
- apache2< 2.4.46-5
- debian_linuxEOL9.0 | 10.0
Alpine1 product
- apache2< 2.4.48-r0
Apache1 product
- http_server1.15.17 | 2.4.47
Apache software foundation1 product
- apache http server2.4.47
Fedoraproject1 product
- fedoraEOL33 | 34
6 vendors · 9 products
References
16 links- lists.apache.org/thread.html/…Mailing List
- lists.apache.org/thread.html/…Mailing List
- lists.fedoraproject.org/archives/…Vendor Advisory
- lists.fedoraproject.org/archives/…Vendor Advisory
Show all 16 references
- security.netapp.com/advisory/ntap-20210727-0008/Third Party Advisory
- www.openwall.com/lists/oss-security/2024/03/13/2Mailing List
