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Weakness · BaseCWE-444

CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

KEV-linkedBase

As of 2026-10-05, CWE-444 (HTTP Request/Response Smuggling) underlies 8 CVEs tracked by Threadlinqs, 1 of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 17 tracked threats.

CVEs
8Mapped to CWE-444
CISA KEV
1Exploited in the wild
Critical
1CVSS v3 critical CVEs
Threats
17Tracked campaigns citing it
Likelihood
—MITRE likelihood of exploit

Last updated:

What is CWE-444?

The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

HTTP requests or responses ("messages") can be malformed or unexpected in ways that cause web servers or clients to interpret the messages in different ways than intermediary HTTP agents such as load balancers, reverse proxies, web caching proxies, application firewalls, etc. For example, an adversary may be able to add duplicate or different header fields that a client or server might interpret as one set of messages, whereas the intermediary might interpret the same sequence of bytes as a different set of messages. For example, discrepancies can arise in how to handle duplicate headers like two Transfer-encoding (TE) or two Content-length (CL), or the malicious HTTP message will have different headers for TE and CL. The inconsistent parsing and interpretation of messages can allow the adversary to "smuggle" a message to the client/server without the intermediary being aware of it. This weakness is usually the result of the usage of outdated or incompatible HTTP protocol versions in the HTTP agents.

CWE-444 is a base-level weakness in MITRE’s Common Weakness Enumeration. Applicable platforms: Not Language-Specific; Web Based; Web Server.

Source: MITRE CWE (CWE-444 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data.

Consequences

  • Integrity, Non-Repudiation, Access Control — Unexpected State, Hide Activities, Bypass Protection Mechanism. An attacker could create HTTP messages to exploit a number of weaknesses including 1) the message can trick the web server to associate a URL with another URL's webpage and caching the contents of the webpage (web cache poisoning attack), 2) the message can be structured to bypass the firewall protection mechanisms and gain unauthorized access to a web application, and 3) the message can invoke a script or a page that returns client credentials (similar to a Cross Site Scripting attack).

Source: MITRE CWE, common consequences.

How CWE-444 is exploited in the wild

Threadlinqs maps 8 CVEs to CWE-444, published between 2025-10-12 and 2026-09-27. 1 is listed in CISA’s Known Exploited Vulnerabilities catalog, the authoritative record of exploitation in the wild, and 1 is tied to ransomware campaigns. By CVSS v3 severity the set splits into 1 critical, 2 high, 2 medium. The highest EPSS score in the set is 97.5% (CVE-2025-61884), the modelled probability of exploitation in the next 30 days. 17 tracked threats reference CWE-444 directly or through a CVE it covers; the most recent is “Apple iCloud Mail Parser Flaws Let Free Accounts Spoof Any @icloud.com Sender and Pass SPF/DKIM/DMARC” (2026-10-04). Affected products concentrate in Citrix NetScaler (1), IBM (1), Kludex (1), among 7 vendors in total.

Vulnerabilities (CVEs)

All 8 CVEs mapped to CWE-444, CISA KEV first, then by CVSS score.

Affected vendors

  • Citrix NetScaler — 1 CVE
  • IBM — 1 CVE
  • Kludex — 1 CVE
  • Oracle Corporation — 1 CVE
  • SAP_SE — 1 CVE
  • elixir-mint — 1 CVE
  • python-hyper — 1 CVE

Threat activity

17 tracked threats cite CWE-444:

Mitigations

  • Implementation: Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433].
  • Implementation: Use only SSL communication.
  • Implementation: Terminate the client session after each request.
  • System Configuration: Turn all pages to non-cacheable.

Source: MITRE CWE, potential mitigations.

Detection methods (MITRE CWE)

  • Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher.