VDB-428208 · CVE-2026-55458 · GCVE-0-2026-55458

Caddy WebSocket Upgrade reverseproxy.go handleUpgradeResponse request smuggling

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.3	$0-$5k	0.00

Summaryinfo

A vulnerability was found in Caddy and classified as problematic. Affected by this vulnerability is the function handleUpgradeResponse of the file modules/caddyhttp/reverseproxy/reverseproxy.go of the component WebSocket Upgrade. The manipulation results in request smuggling. This vulnerability was named CVE-2026-55458. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in Caddy (the affected version is unknown). It has been classified as problematic. Affected is the function handleUpgradeResponse of the file modules/caddyhttp/reverseproxy/reverseproxy.go of the component WebSocket Upgrade. The manipulation with an unknown input leads to a request smuggling vulnerability. CWE is classifying the issue as 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. This is going to have an impact on integrity.

This vulnerability is traded as CVE-2026-55458. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 10/28/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

Caddy

CPE 2.3info

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CPE 2.2info

🔒

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.3
VulDB Meta Temp Score: 5.3

VulDB Base Score: 5.3
VulDB Temp Score: 5.3
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Request smuggling
CWE: CWE-444
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

10/28/2026 Advisory disclosed
10/28/2026 +0 days VulDB entry created
10/28/2026 +0 days VulDB entry last update

Sourcesinfo

Status: Not defined

CVE: CVE-2026-55458 (🔒)

GCVE (CVE): GCVE-0-2026-55458
GCVE (VulDB): GCVE-100-428208

Entryinfo

Created: 10/28/2026 21:33
Changes: 10/28/2026 21:33 (48)
Complete: 🔍
Cache ID: 216::103