CVE-2026-44649: SillyTavern has Authentication Bypass via SSO Header Injection

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.3%, percentile 21: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 21% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes sillytavern (npm) <= 1.17.0, fixed in 1.18.0. Check your lockfile, including transitive dependencies.

What it is

SillyTavern is a locally installed user interface that allows users to interact with text generation large language models, image generation engines, and text-to-speech voice models. Prior to 1.18.0, SillyTavern accepts Remote-User (Authelia) and X-Authentik-Username (Authentik) HTTP headers to automatically log in users when SSO is configured. There is no validation that these headers originate from a trusted reverse proxy. Any network client that can reach the SillyTavern port directly can inject these headers and authenticate as any user, including administrators, without a password. This vulnerability is exploitable only when sso.autheliaAuth: true or sso.authentikAuth: true is set in config.yaml (both default to false). This vulnerability is fixed in 1.18.0.

From the GitHub advisory

Resolution

SillyTavern 1.18.0 now includes a configuration option to limit which IP addresses can authorize using SSO headers, limiting to just loopback addresses by default. A setting can be customized according to user's needs.

Documentation: https://docs.sillytavern.app/administration/sso/

Summary

SillyTavern accepts Remote-User (Authelia) and X-Authentik-Username (Authentik) HTTP headers to automatically log in users when SSO is configured. There is no validation that these headers originate from a trusted reverse proxy. Any network client that can reach the SillyTavern port directly can inject these headers and authenticate as any user, including administrators, without a password. This vulnerability is exploitable only when sso.autheliaAuth: true or sso.authentikAuth: true is set in config.yaml (both default to false).

Weakness type: CWE-290, CWE-306, CWE-346, CWE-807.

Product: sillytavern (npm) · Assigned by: GitHub_M · Published: 2026-05-29

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.29% probability of exploitation activity in the next 30 days; percentile 21.

Timeline

• 2026-05-12 — GitHub-reviewed advisory GHSA-gxx6-h3g6-vwjh published (critical)
• 2026-05-29 — CVE record published by GitHub_M
• 2026-06-02 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-gxx6-h3g6-vwjh github.com
2. CVE.org record CVE-2026-44649 cve.org
3. NVD entry CVE-2026-44649 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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