CVE-2021-41524 [High] | Denial of Service in Http Server

CVE-2021-41524 is rated High Risk (69.2/100): CVSS High severity, with high exploitation likelihood (EPSS 24.98%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +21.02% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	3.96%	24.98%	+21.02%
2	2026-05-26	7.10%	3.96%	-3.14%
3	2025-11-21	—	7.10%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

3.96%

24.98%

+21.02%

2026-05-26

7.10%

3.96%

-3.14%

2025-11-21

—

7.10%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
5.0	2.0	MEDIUM	`AV:N/AC:L/Au:N/C:N/I:N/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	10.0	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

5.0

2.0

MEDIUM

AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

2.9

[email protected]

OS Trackers for CVE-2021-41524

vendor	priority	summary	link
`alpine`	high	CVE-2021-41524: 1 source package rows (apache2); 9 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 9, open 0.	https://security.alpinelinux.org/vuln/CVE-2021-41524
`debian`	unimportant	CVE-2021-41524 unimportant priority: Debian including 1 source packages (apache2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-41524
`gentoo`	high	CVE-2021-41524: 1 GLSA(s) (202208-20), 2 atom(s) (app-admin/apache-tools, www-servers/apache); latest impact high.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-41524
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-41524
`ubuntu`	medium	CVE-2021-41524 medium priority: Ubuntu including 1 source packages (apache2), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 7, released 1.	https://ubuntu.com/security/CVE-2021-41524

Affected software / configurations for CVE-2021-41524

Vendor	Product	Version	Raw CPE
apache	http_server	2.4.49	cpe:2.3:a:apache:http_server:2.4.49:::::::*
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*
fedoraproject	fedora	35	cpe:2.3:o:fedoraproject:fedora:35:::::::*
oracle	instantis_enterprisetrack	17.1	cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:::::::*
oracle	instantis_enterprisetrack	17.2	cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:::::::*
oracle	instantis_enterprisetrack	17.3	cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:::::::*
netapp	cloud_backup	—	cpe:2.3:a:netapp:cloud_backup:-:::::::*

References for CVE-2021-41524

URL	Tags
http://www.openwall.com/lists/oss-security/2021/10/05/1	Mailing List Third Party Advisory
https://httpd.apache.org/security/vulnerabilities_24.html	Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DSM6UWQICBJ2TU727RENU3HBKEAFLT6T/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EUVJVRJRBW5QVX4OY3NOHZDQ3B3YOTSG/
https://security.gentoo.org/glsa/202208-20	Third Party Advisory
https://security.netapp.com/advisory/ntap-20211029-0009/	Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-pathtrv-LAzg68cZ	Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html	Patch Third Party Advisory

URL

CVE-2021-41524 | null pointer dereference in h2 fuzzing

Exploit prediction scoring system (EPSS) score for CVE-2021-41524

Common vulnerability scoring system (CVSS) metrics for CVE-2021-41524

Weakness enumeration for CVE-2021-41524

OS Trackers for CVE-2021-41524

Affected software / configurations for CVE-2021-41524

References for CVE-2021-41524