How severe is CVE-2021-26690?

CVE-2021-26690 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-26690 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 65% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26690?

CVE-2021-26690 primarily affects Apache Http Server. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-26690?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-26690 published?

CVE-2021-26690 was published on 2021-06-10 and last updated on 2026-06-17.

CVE-2021-26690

CVE-2021-26690 is a high-severity vulnerability in Apache Http Server with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 65% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 65% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-476
Affected product: Apache Http Server
Published: 2021-06-10
Last modified: 2026-06-17

Description

Apache HTTP Server versions 2.4.0 to 2.4.46 A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference and crash, leading to a possible Denial Of Service

Frequently asked questions

What is CVE-2021-26690?: Apache HTTP Server versions 2.4.0 to 2.4.46 A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference and crash, leading to a possible Denial Of Service
How severe is CVE-2021-26690?: CVE-2021-26690 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-26690 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 65% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26690?: CVE-2021-26690 primarily affects Apache Http Server. In total, 10 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26690?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-26690 published?: CVE-2021-26690 was published on 2021-06-10 and last updated on 2026-06-17.

References

Affected products (10)

cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
cpe:2.3:a:oracle:enterprise_manager_ops_center:12.4.0.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.2:*:*:*:*:*:*:*
cpe:2.3:a:oracle:instantis_enterprisetrack:17.3:*:*:*:*:*:*:*
cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*

More vulnerabilities in Apache Http Server

CVE-2010-0425 — Critical (CVSS 10.0): modules/arch/win32/mod_isapi.c in mod_isapi in the Apache HTTP Server 2.0.37 through 2.0.63, 2.2.0 through 2.2.14, and…
CVE-2005-2700 — Critical (CVSS 10.0): ssl_engine_kernel.c in mod_ssl before 2.8.24, when using "SSLVerifyClient optional" in the global virtual host…
CVE-2004-0492 — Critical (CVSS 10.0): Heap-based buffer overflow in proxy_util.c for mod_proxy in Apache 1.3.25 to 1.3.31 allows remote attackers to cause a…
CVE-2003-0789 — Critical (CVSS 10.0): mod_cgid in Apache before 2.0.48, when using a threaded MPM, does not properly handle CGI redirect paths, which could…
CVE-1999-1293 — Critical (CVSS 10.0): mod_proxy in Apache 1.2.5 and earlier allows remote attackers to cause a denial of service via malformed FTP commands,…
CVE-1999-0926 — Critical (CVSS 10.0): Apache allows remote attackers to conduct a denial of service via a large number of MIME headers.

All CVEs affecting Apache Http Server →

Other CWE-476 (NULL Pointer Dereference) vulnerabilities

CVE-2022-36648 — Critical (CVSS 10.0): The hardware emulation in the of_dpa_cmd_add_l2_flood of rocker device model in QEMU, as used in 7.0.0 and earlier,…
CVE-2020-14500 — Critical (CVSS 10.0): Secomea GateManager all versions prior to 9.2c, An attacker can send a negative value and overwrite arbitrary data.
CVE-2010-2495 — Critical (CVSS 10.0): The pppol2tp_xmit function in drivers/net/pppol2tp.c in the L2TP implementation in the Linux kernel before 2.6.34 does…
CVE-2026-46195 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: smb: client: validate dacloffset before building…
CVE-2026-31657 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: batman-adv: hold claim backbone gateways by…
CVE-2026-31436 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: dmaengine: idxd: fix possible wrong descriptor…

Browse all CWE-476 (NULL Pointer Dereference) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

50.255.62.89 (ipv4-addr)
147.15.15.226 (ipv4-addr)
45.84.120.3 (ipv4-addr)
61.76.112.4 (ipv4-addr)
60.199.224.2 (ipv4-addr)
46.253.45.10 (ipv4-addr)
45.232.73.84 (ipv4-addr)
45.120.115.150 (ipv4-addr)