CVE-2026-34227Public exploitNetwork attack vector

C2 session takeover via unauthenticated MCP interface

Published Mar 31, 2026 · Updated Mar 31, 2026

Authentication bypass in Bishop Fox Sliver before 1.7.4 allows remote attackers to control active C2 sessions through an operator's browser. The client-side MCP service omits authentication and origin restrictions, while its text/plain handling lets cross-origin requests avoid browser preflight. An operator must visit an attacker-controlled page unless the service is bound beyond localhost; exploitation exposes target data and file operations across connected implants.

CVSS severity5.9
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Bishop Fox Sliver before 1.7.4 allows remote attackers to control active C2 sessions through an operator's browser. The client-side MCP service omits authentication and origin restrictions, while its text/plain handling lets cross-origin requests avoid browser preflight. An operator must visit an attacker-controlled page unless the service is bound beyond localhost; exploitation exposes target data and file operations across connected implants.

The record

CVE
CVE-2026-34227
Published
Mar 31, 2026
Updated
Mar 31, 2026
Vendor
Bishop Fox
Product
Sliver
Classifications
CWE-306, CWE-942, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 31, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.7.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Bishop Fox · Sliverversion=< 1.7.4

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
5.9GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-306Missing Authentication for Critical Function
CWE-942Permissive Cross-domain Security Policy with Untrusted Domains
T1189Drive-by Compromise

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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