VulnerabilityPublished 4 Dec 2025Updated 8 Dec 2025

CVE-2025-66373: HTTP Request/Response Smuggling

Source CVE Database V5

Not known to be exploited · CVSS 4.8 Medium.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 17% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

Monitor Akamai's official advisories and apply patches or updates to Akamai Ghost as soon as they become available to address this vulnerability.
Review and harden origin server configurations to reject or safely handle malformed chunked HTTP requests, minimizing the risk of request smuggling.
Implement strict input validation and HTTP request parsing on origin servers to detect and block suspicious chunked transfer encoding anomalies.
Employ Web Application Firewalls (WAFs) with updated rules capable of detecting HTTP request smuggling attempts.
Conduct regular security assessments and penetration testing focusing on HTTP request smuggling scenarios to identify potential weaknesses.
Consider deploying additional monitoring and anomaly detection on CDN traffic to identify unusual request patterns indicative of exploitation attempts.
Coordinate with Akamai support to understand any interim mitigations or configuration changes that can reduce exposure before patches are applied.

Description

Akamai Ghost on Akamai CDN edge servers before 2025-11-17 has a chunked request body processing error that can result in HTTP request smuggling. When Akamai Ghost receives an invalid chunked body that includes a chunk size different from the actual size of the following chunk data, under certain circumstances, Akamai Ghost erroneously forwards the invalid request and subsequent superfluous bytes to the origin server. An attacker could hide a smuggled request in these superfluous bytes. Whether this is exploitable depends on the origin server's behavior and how it processes the invalid request it receives from Akamai Ghost.

Impact

For European organizations relying on Akamai CDN services, this vulnerability could allow attackers to perform HTTP request smuggling attacks, potentially bypassing security controls, injecting unauthorized requests, or manipulating web traffic confidentiality and integrity. This could lead to session hijacking, cache poisoning, web application firewall bypass, or unauthorized access to sensitive data. The impact is particularly concerning for organizations handling sensitive or regulated data, such as financial institutions, healthcare providers, and government agencies. However, the actual impact depends on the origin server's behavior and its ability to handle malformed chunked requests securely. Since the vulnerability does not affect availability directly and requires high attack complexity, the risk is moderate but should not be underestimated given the widespread use of Akamai CDN in Europe.

Summary

CVE-2025-66373 is a vulnerability in Akamai Ghost, a component running on Akamai CDN edge servers, that mishandles HTTP chunked transfer encoding. Specifically, when Akamai Ghost receives an HTTP request with a chunked body where the declared chunk size differs from the actual size of the chunk data, it incorrectly forwards the malformed request along with additional superfluous bytes to the origin server. This behavior can be exploited for HTTP request smuggling (CWE-444), where an attacker crafts a request that is interpreted differently by the CDN and the origin server, allowing the attacker to inject hidden or smuggled requests. The success of such an attack depends on the origin server's parsing logic and its tolerance for malformed chunked requests. The vulnerability has a CVSS v3.1 base score of 4.8, indicating medium severity, with network attack vector, high attack complexity, no privileges required, no user interaction, and impacts on confidentiality and integrity but not availability. No public exploits are known yet, and no patches have been linked, suggesting that mitigation currently relies on monitoring and configuration hardening. The vulnerability was published on December 4, 2025, and affects versions of Akamai Ghost prior to November 17, 2025.

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
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.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 11 Dec 2025, 21:57 UTC

WeaknessesCWE-444

Technical details

References

Community reviews

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