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HTTP ServerWeb server / proxy · Apache

CVE-2016-2161

HIGH · 7.5 CVSS v3.0 Published 2017-07-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A denial-of-service vulnerability in mod_auth_digest in Apache HTTP Server versions 2.4.0 through 2.4.23 allows remote attackers to cause a process crash with malicious input. The critical issue is that the crash state persists, causing subsequent valid requests to also crash the process, creating a permanent denial-of-service condition.

MitigationUpgrade Apache HTTP Server to version 2.4.24 or later, which contains the fix for this vulnerability in mod_auth_digest.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
HTTP ServerWeb server / proxy
Affected:= 2.4.0= 2.4.1= 2.4.2= 2.4.3= 2.4.6= 2.4.7= 2.4.8= 2.4.9= 2.4.10= 2.4.12= 2.4.14= 2.4.16

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Apache HTTP Server version
    Run 'httpd -v' or 'apache2 -v' to display the installed version, or query the package manager with 'rpm -q httpd' or 'dpkg -l apache2'
    Affected if The installed version is 2.4.0 through 2.4.23 (including 2.4.0, 2.4.1, 2.4.2, 2.4.3, 2.4.6, 2.4.7, 2.4.8, 2.4.9, 2.4.10, 2.4.12, 2.4.14, or 2.4.16)
  2. Verify if mod_auth_digest module is loaded
    Search Apache configuration files for 'LoadModule auth_digest_module' directive, typically in httpd.conf, apache2.conf, or files in the conf-enabled directory
    Affected if The mod_auth_digest module is loaded (LoadModule auth_digest_module directive is present and uncommented)
  3. Confirm Digest authentication is configured
    Search configuration files for 'AuthType Digest' or any AuthDigest* directives that enable Digest authentication for protected resources
    Affected if Digest authentication (AuthType Digest) is actively configured for any directory, location, or virtual host

The environment is affected if Apache version 2.4.0 through 2.4.23 is running with mod_auth_digest enabled and Digest authentication configured, as only that combination triggers the vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Apache HTTP Server to version 2.4.24 or later, which contains the fix for this vulnerability in mod_auth_digest.

Fix this in HTTP Server Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2016-2161 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data