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CVE-2024-38475Apache HTTP Server Improper Escaping of Output Vulnerability

Patch nowCritical9.1Exploited, CISA due date 2025-05-22EPSS 100%, higher than 100% of scored CVEs

CVE-2024-38475 is a improper output encoding in Apache HTTP Server, rated critical (9.1 on CVSS 3.1).

Why this priority: Exploited in the wild: listed in CISA's KEV catalog.

Published · Updated · NVD status: Analyzed

What it is

Output is not encoded for where it lands, so data can be read as markup or commands.

How it is reached

An attacker can exploit it over the network, without an account, and nobody has to click anything.

What an attacker gains

A successful attack can read the data it protects and change data or behaviour. In practice, this kind of flaw lets an attacker act inside a signed-in user's browser session.

Is it being exploited?

CISA added it to the Known Exploited Vulnerabilities catalog on 2025-05-01: it is being exploited in the wild. It can be exploited automatically, at scale. EPSS estimates a 100% chance of exploitation activity in the next 30 days, higher than 100% of scored CVEs.

What to do

  1. Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2025-05-22.
  2. Upgrade Apache HTTP Server to 2.4.60 or later. Other affected products have their own fixed versions on this page. The patch notes are linked below.
  3. Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
  4. Check exposed instances for signs of compromise, not only for the version.

Description from NVD

Improper escaping of output in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows an attacker to map URLs to filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any URL, resulting in code execution or source code disclosure.

Substitutions in server context that use a backreferences or variables as the first segment of the substitution are affected.  Some unsafe RewiteRules will be broken by this change and the rewrite flag "UnsafePrefixStat" can be used to opt back in once ensuring the substitution is appropriately constrained.

What this means for your architecture.

A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.

Components it touches

  • Network edge devices: VPNs, firewalls, routers and gateways. They sit between the internet and internal networks, so a flaw in one is often the first step into everything behind it.
  • Operating systems on servers, workstations or devices. Everything on the host inherits the flaw.
  • Web front ends and single-page apps. The flaw sits between a user's browser and the web application.
  • Admin consoles served to a browser. The flaw sits between a user's browser and the web application.

Trust boundaries in play

  • Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
  • Between a user's browser and the web application. An attacker who crosses it can act inside a signed-in user's browser session.

Questions to answer about your own systems

  • Where does Apache HTTP Server run in your systems, and at which version?
  • Which of those instances can be reached from the internet or partner networks?
  • What can it reach once compromised: which data stores, secrets and services?
See how Veriom maps an architectureTake the interactive tour

Read more

Sources

  • CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
  • Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
  • Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
  • Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.