CVE-2016-2161

CVE-2016-2161 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 21% places it in the 97th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-20.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v2: 5.0
• EPSS exploit prediction: 21% (97th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-20
• Affected product: Apache Http Server
• Published: 2017-07-27
• Last modified: 2026-06-17

Description

In Apache HTTP Server versions 2.4.0 to 2.4.23, malicious input to mod_auth_digest can cause the server to crash, and each instance continues to crash even for subsequently valid requests.

Frequently asked questions

What is CVE-2016-2161?

In Apache HTTP Server versions 2.4.0 to 2.4.23, malicious input to mod_auth_digest can cause the server to crash, and each instance continues to crash even for subsequently valid requests.

How severe is CVE-2016-2161?

CVE-2016-2161 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-2016-2161 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 21% (97th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-2161?

CVE-2016-2161 primarily affects Apache Http Server. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-2161?

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-2016-2161 published?

CVE-2016-2161 was published on 2017-07-27 and last updated on 2026-06-17.

References

• http://rhn.redhat.com/errata/RHSA-2017-1415.html
• http://www.debian.org/security/2017/dsa-3796
• http://www.securityfocus.com/bid/95076
• http://www.securitytracker.com/id/1037508
• https://access.redhat.com/errata/RHSA-2017:0906
• https://access.redhat.com/errata/RHSA-2017:1161
• https://access.redhat.com/errata/RHSA-2017:1413
• https://access.redhat.com/errata/RHSA-2017:1414
• https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03725en_us
• https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2016-2161
• https://lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rd336919f655b7ff309385e34a143e41c503e133da80414485b3abcc9%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/re3d27b6250aa8548b8845d314bb8a350b3df326cacbbfdfe4d455234%40%3Ccvs.httpd.apache.org%3E
• https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E
• https://security.gentoo.org/glsa/201701-36
• https://security.netapp.com/advisory/ntap-20180423-0001/
• https://support.apple.com/HT208221
• https://www.tenable.com/security/tns-2017-04

Affected products (17)

• cpe:2.3:a:apache:http_server:2.4.0:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.1:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.2:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.3:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.6:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.7:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.8:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.9:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.10:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.12:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.14:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.16:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.19:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.20:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.21:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.22:*:*:*:*:*:*:*
• cpe:2.3:a:apache:http_server:2.4.23:*:*:*:*:*:*:*

More vulnerabilities in Apache Http Server

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• 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-20 (Improper Input Validation) vulnerabilities

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• CVE-2026-48281 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
• CVE-2026-48277 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
• CVE-2026-48055 — Critical (CVSS 10.0): Streambert is a cross-platform Electron Desktop App to stream and download any video media. In versions 2.4.0 and…
• CVE-2026-34910 — Critical (CVSS 10.0): A malicious actor with access to the network could exploit an Improper Input Validation vulnerability found in UniFi OS…
• CVE-2026-33587 — Critical (CVSS 10.0): Lack of user input sanitisation in Open Notebook v1.8.3 allows the application user to execute Python code (and…

Browse all CWE-20 (Improper Input Validation) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

• 45.84.120.3 (ipv4-addr)
• 61.76.112.4 (ipv4-addr)
• 45.232.73.84 (ipv4-addr)
• 41.205.23.59 (ipv4-addr)
• 203.192.232.180 (ipv4-addr)
• 189.15.10.179 (ipv4-addr)
• 187.110.238.50 (ipv4-addr)
• 182.93.50.90 (ipv4-addr)