Sliver has DNS C2 OTP Bypass that Allows Unauthenticated Session Flooding and Denial of Service

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-25791: 0.45% estimated exploitation activity in the next 30 days; percentile 39.41 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The DNS C2 listener accepts unauthenticated TOTP bootstrap messages and allocates server-side DNS sessions without validating OTP values, even when EnforceOTP is enabled. Because sessions are stored without a cleanup/expiry path in this flow, an unauthenticated remote actor can repeatedly create sessions and drive memory exhaustion. Vulnerable Component - server/c2/dns.go:84-90 (EnforceOTP stored but not enforced in bootstrap) - server/c2/dns.go:378-390 (TOTP requests routed directly to bootstrap) - server/c2/dns.go:490-521 (handleHello allocates session without OTP validation) - server/c2/dns.go:495 (sessions.Store with no lifecycle control in this path) - client/command/jobs/dns.go:46-52 (operator-facing EnforceOTP control implies auth gate) - implant/sliver/transports/dnsclient/dnsclient.go:896-900 (otpMsg sends TOTP with ID=0) - protobuf/dnspb/dns.proto:22 (documents TOTP in ID field) Attack Vector - Network-accessible DNS listener - No authentication required -…

Published by the source

6 Feb 2026, 22:52 UTC

Last modified by the source

9 Feb 2026, 22:39 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wxrw-gvg8-fqjp

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# Patch Next advisory brief: CVE-2026-25791

Advisory: Sliver has DNS C2 OTP Bypass that Allows Unauthenticated Session Flooding and Denial of Service
IDs: CVE-2026-25791, GHSA-wxrw-gvg8-fqjp
Record: https://patchnext.com/advisories/cve-2026-25791 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/bishopfox/sliver 1.6.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/bishopfox/sliver: affected <= 1.6.11; fixed in 1.6.12

## Suggested inspection (read-only)
- Go github.com/bishopfox/sliver: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/bishopfox/sliver.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-wxrw-gvg8-fqjp (GitHub-reviewed advisory GHSA-wxrw-gvg8-fqjp lists affected ranges: Go github.com/bishopfox/sliver >=0 <=1.6.11)

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