dbcve.org
HTTP ServerWeb server / proxy · Apache

CVE-2025-49812

HIGH · 7.4 CVSS v3.1 Published 2025-07-10
Fix available
A fix is available. Upgrade to 2.4.64 or later.
See remediation →
83/100
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 some mod_ssl configurations on Apache HTTP Server versions through to 2.4.63, an HTTP desynchronisation attack allows a man-in-the-middle attacker to hijack an HTTP session via a TLS upgrade. Only configurations using "SSLEngine optional" to enable TLS upgrades are affected. Users are recommended to upgrade to version 2.4.64, which removes support for TLS upgrade.

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

An HTTP desynchronization vulnerability in mod_ssl affects Apache HTTP Server versions through 2.4.63 when using 'SSLEngine optional' to enable TLS upgrades. A man-in-the-middle attacker can hijack HTTP sessions by manipulating the TLS upgrade handshake, causing desynchronization between client and server state.

MitigationUpgrade to Apache HTTP Server 2.4.64 which removes TLS upgrade support, or disable 'SSLEngine optional' configurations to prevent TLS upgrades.

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:< 2.4.64

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

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 'apache2 -v' (Debian/Ubuntu) or 'httpd -v' (RHEL/CentOS) to determine the installed version
    Affected if Version is 2.4.63 or earlier (any version < 2.4.64)
  2. Verify mod_ssl module is loaded
    Run 'apache2ctl -M | grep ssl' or 'httpd -M | grep ssl' to confirm mod_ssl is active
    Affected if mod_ssl module is present in the loaded modules list
  3. Search for SSLEngine optional directive
    Search SSL configuration files (commonly /etc/apache2/mods-available/ssl.conf, /etc/httpd/conf.d/ssl.conf, or SSL virtual host config files) for the string 'SSLEngine optional' using grep -r
    Affected if The directive 'SSLEngine optional' is found in any Apache SSL configuration file
  4. Identify SSL virtual host configurations
    Review all virtual host configuration files containing SSL settings (typically in /etc/apache2/sites-enabled/ or /etc/httpd/conf.d/) and check if any use SSLEngine optional
    Affected if Any SSL-enabled virtual host uses 'SSLEngine optional' instead of 'SSLEngine on' or 'SSLEngine off'

User is affected if running Apache HTTP Server version < 2.4.64 with mod_ssl loaded AND 'SSLEngine optional' is configured in any SSL virtual host or configuration file.

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.

dbcve · scoped
Upgrade available Upgrade to 2.4.64 or later
Fixed in 2.4.64
Interim mitigation

Upgrade to Apache HTTP Server 2.4.64 which removes TLS upgrade support, or disable 'SSLEngine optional' configurations to prevent TLS upgrades.

Recommended fix High confidence

2.4.64

  1. Check current Apache HTTP Server version (e.g., `apache2 -v` or `httpd -v`)
  2. Stop the Apache service (e.g., `systemctl stop apache2` or `systemctl stop httpd`)
  3. Upgrade Apache HTTP Server to version 2.4.64 using your package manager or by compiling from source (e.g., `apt-get update && apt-get install apache2` on Debian/Ubuntu, or `yum update httpd` on RHEL/CentOS)
  4. Verify the upgrade was successful by checking the installed version (`apache2 -v` or `httpd -v`)
  5. Ensure any SSL/TLS configuration is reviewed - note that "SSLEngine optional" is no longer supported and should be changed to "SSLEngine on" or "SSLEngine off" as appropriate for your configuration
  6. Start the Apache service (e.g., `systemctl start apache2` or `systemctl start httpd`)
  7. Verify the server is running and functioning correctly
Caveat TLS upgrade via "SSLEngine optional" is no longer supported; configurations using this directive must be updated to use "SSLEngine on" for SSL/TLS or "SSLEngine off" for non-SSL

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in HTTP Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,180
Get the upgrade done

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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-2025-49812 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