How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

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359,079

Total vulnerabilities in the database

actix-http has HTTP/1.1 CL.TE Request Smuggling — actix-http

Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')

A vulnerability in actix-http's HTTP/1.1 request parser allows an unauthenticated remote client to smuggle requests in deployments where a front-end HTTP intermediary and the Actix backend disagree about whether Content-Length or Transfer-Encoding: chunked defines the request body length.

Severity

Medium. This is an HTTP request smuggling vulnerability that can be triggered over the network without application-level credentials. Exploitation requires a specific proxy topology: an upstream proxy, WAF, load balancer, or similar intermediary must use Content-Length framing while forwarding the conflicting Transfer-Encoding: chunked request to an Actix backend over a reused HTTP/1.1 connection.

Affected Versions

actix-http: versions up to and including 3.12.0

Description

HTTP/1.1 requests that contain both Content-Length and Transfer-Encoding: chunked are ambiguous and must be rejected by recipients to avoid request smuggling.

Affected versions of actix-http accepted a request with a syntactically valid Content-Length header and Transfer-Encoding: chunked on the same HTTP/1.1 message. The parser then selected chunked decoding instead of rejecting the conflicting framing signals.

In a CL.TE proxy topology, an intermediary may treat bytes after the declared Content-Length body as part of the first request, while the Actix backend stops at the terminating chunk marker and parses the remaining bytes on the backend connection as a second HTTP request. This creates a backend-side request desynchronization primitive.

The issue is limited to HTTP/1.1 request parsing.

Impact

HTTP request smuggling

Attack Vector: Network, unauthenticated.
Effect: Backend request desynchronization with low integrity impact to requests processed by the vulnerable Actix service.
Scope: Actix services using affected actix-http versions behind an HTTP/1.1 intermediary that forwards ambiguous Content-Length plus Transfer-Encoding: chunked requests and reuses backend connections.

No direct confidentiality, availability, or subsequent-system impact is scored for this advisory.

Fixed Versions

This issue is fixed in actix-http 3.12.1.

The fix rejects HTTP/1.1 requests that contain both Content-Length and Transfer-Encoding: chunked instead of choosing one framing interpretation.

Mitigation

Users should upgrade to actix-http 3.12.1 or later.

Applications that depend on actix-http through actix-web, awc, or another Actix crate should ensure dependency resolution selects actix-http 3.12.1 or later. For example:

cargo update -p actix-http

If an immediate upgrade is not possible, configure all upstream HTTP intermediaries to reject HTTP/1.1 requests that contain both Content-Length and Transfer-Encoding, and avoid forwarding ambiguous request framing to Actix backends.

Credits

Actix thanks mufeedvh who disclosed this issue through coordinated disclosure.

Published: Apr 22, 2026
Updated: Apr 23, 2026
GHSA: GHSA-xhj4-vrgc-hr34
Severity: Medium
Exploit:
CISA KEV:

No technical information available.

CWEs:

CWE-444

Affected Software
References

Software	From	Fixed in
actix-http	-	3.12.1

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.