CVE WatchSep 21, 2026

CVE-2026-87858

Temporal Server decided whether a Workflow completion callback was internal by reading a caller-supplied HTTP header. An authenticated calle

CVSS

—

No CVSS

EPSS

—

KEV

—

Exploit Today

0-100

Published: Sep 21, 2026 · Last modified: Sep 21, 2026 · CWE-807

EPSS · 30d

Not enough EPSS history yet.

Technical description

Temporal Server decided whether a Workflow completion callback was internal by reading a caller-supplied HTTP header. An authenticated caller holding only write permission in a single namespace could attach a completion callback whose URL host matched the configured callback address allowlist, whose URL path was any Temporal HTTP API route, and whose header map contained a non-empty header named source. When the History service delivered that callback, the non-empty source header caused it to re-target the request at the local frontend client and rewrite only the scheme and host, preserving the caller's path, query, and request body. Where an internal frontend is deployed with its HTTP API enabled, that client resolves to the internal frontend, which authorizes every request as a system administrator without requiring authentication information. The result is that the server performs an attacker-chosen state-changing HTTP POST against its own administrative API on the caller's behalf, in namespaces where the caller has no permission. The caller never needs network access to the internal frontend, because the History service makes the request. Confirmed effects include terminating Workflows in other namespaces, registering namespaces, modifying another namespace's configuration, and deleting another namespace and its Workflows. The affected routing logic is present in both the HSM and CHASM callback delivery implementations. This description and the CVSS score in this record describe releases 1.30.0 and later, where any non-empty source header is sufficient. Releases 1.25.0 through 1.29.7 are affected by a narrower form of the same defect in which the header must exactly match a configured cluster ID, a UUID that a namespace-scoped caller cannot read through the API. The consequence once that match occurs is the same, but the attack is materially harder and scores lower. To determine whether a deployment is affected, check two settings together: the static Server configuration for a non-zero services.internal-frontend.rpc.httpPort, and the effective per-namespace dynamic configuration value of component.callbacks.allowedAddresses. A deployment is exposed only when an internal frontend is deployed with a non-zero HTTP port, at least one allowlist rule admits a host, and authorization is enabled. The allowlist is empty by default, which denies all external callback URLs, and the stock static topology does not include an internal frontend. Note that a failed attach returns the error 'invalid url: url does not match any configured callback address', which proves only that one tested URL did not match and does not prove the effective allowlist is empty. To look for callbacks already attached, use DescribeWorkflowExecution, which returns callback information for a Workflow's registered completion callbacks. Operators should be aware of a gap when searching for evidence of delivery: the frontend HTTP API server records the request method and URL at debug level only, so at default log levels a delivered request is not written to the internal frontend's logs, and the absence of such log entries is not evidence that the issue was not exploited.

Official references

Related CVEs

CVECVSSEPSSKEVRExploitTitleMod.

CVE-2026-857519.8 CRI

—

——0Mailu is a mail server distributed as a set of Docker images. From Mailu 2.0 until 2024.06.55 and prior to Mailu helm-charts 2.7.3, deployments with PROXY_AUTH_WHITELIST configured but REAL_IP_HEADER unset trusted a client-controlled X-Forwarded-By header for header-based proxy authentication. The proxy_hide_header directive in the nginx template at core/nginx/conf/proxy.conf hid the header from upstream responses but did not overwrite the incoming request value in this configuration. An unauthenticated remote attacker could therefore spoof the trusted proxy identity and bypass authentication. This issue is fixed in Mailu 2024.06.55 and Mailu helm-charts 2.7.3.3h CVE-2026-811798.1 HIG

18.5%

——6SysReptor is a fully customizable pentest reporting platform. Prior to 2026.58, installations that enable password reset by email while configuring ALLOWED_HOSTS with a wildcard accept an attacker-controlled Host header when generating a password reset link. An unauthenticated attacker can request a reset email whose link points to an attacker-controlled system, and a victim who follows that link can disclose the reset token, allowing the attacker to reset the victim's password and take over the account. Exploitation also requires a configured email gateway and an email address for the victim, while some reverse proxy configurations may reject the hostile Host header. This issue is fixed in version 2026.58.3d CVE-2026-868639.8 CRI

29.5%

——9pgAdmin 4's Webserver authentication source is intended to accept an identity asserted by the web server or reverse proxy in front of pgAdmin, delivered through the WSGI/CGI environment. WebserverAuthentication.get_user() read config.WEBSERVER_REMOTE_USER from request.environ and, when that returned nothing, fell back to reading the same name directly from the inbound HTTP request headers via request.headers.get(). An inbound HTTP header is written by whoever sends the request, so any client able to reach pgAdmin could supply that header itself and be authenticated as any username it named, including an existing Administrator, without presenting a password or any other credential. The environment lookup could also be satisfied by a client-supplied header whenever WEBSERVER_REMOTE_USER was configured to an HTTP_-prefixed or hyphenated name such as HTTP_X_FORWARDED_USER or X-Forwarded-User, since WSGI servers place inbound headers into the environment under exactly those names. Deployments are affected only when 'webserver' is enabled in AUTHENTICATION_SOURCES. The fix distinguishes a genuine CGI/WSGI variable from a header-derived one and implicitly trusts only the former. A header-asserted identity is now accepted only when the operator explicitly opts in via WEBSERVER_REMOTE_USER_FROM_HEADER, the request arrives from a peer listed in WEBSERVER_TRUSTED_PROXIES, and, when configured, a shared secret supplied in WEBSERVER_SHARED_SECRET_HEADER matches WEBSERVER_SHARED_SECRET under a constant-time comparison. The trusted-peer check deliberately reads the real socket peer address rather than request.remote_addr, because ProxyFix rewrites the latter from the client-controlled X-Forwarded-For header and would otherwise allow an attacker to claim to be the trusted proxy. As defence in depth, login() now refuses any account whose auth_source is not 'webserver', so a misconfigured trust gate cannot be used to assume an internal or LDAP account. This issue affects pgAdmin 4: from 6.2 before 9.18.4h CVE-2026-784274.3 MED

29.4%

——9The NeuVector admission webhook silently excludes containers from policy evaluation when their image path matches one of three hardcoded service mesh sidecar images. Since the image path is entirely controlled by the workload author, any user capable of deploying workloads can evade admission deny rules simply by naming their image path after one of these sidecar images.3d CVE-2026-591576.5 MED

39.1%

——12webhookd is a minimalist webhook server that triggers shell scripts and external processes through HTTP requests. Prior to 1.22.0, webhookd deployments without htpasswd authentication forwarded all incoming HTTP headers through HTTPParamsToShellVars in pkg/api/index.go into the hook script environment without an allowlist. When an upstream reverse proxy did not strip a client-supplied X-WebAuthn-User header and a hook script trusted that variable for identity or privilege, a remote unauthenticated attacker could spoof another user, bypass script security controls, and access or modify resources available to the impersonated identity. This issue is fixed in version 1.22.0.5d CVE-2026-79701—

19.2%

——6Joomla Extension - joomshaper.com - Unauthenticated CAPTCHA Bypass in Module Context in the Contact, Opt-in and Form Builder Addons in SP Page Builder Pro 3.2.6 - 6.9.0 - In the ajax_contact, optin_form and form_builder addons, the result returned by the CAPTCHA plugin's onCheckAnswer event was discarded and replaced with a test for a non-empty string whenever the request-supplied view_type parameter equalled module. Submitting view_type=module together with any arbitrary token value therefore passed verification. This affected every instance of these addons placed inside an SP Page Builder module, irrespective of the CAPTCHA type configured for the site, and the view_type parameter was never validated against the context in which the form was actually rendered.5d