AnyCable: Pusher REST API Does Not Verify Request Body MD5 Enabling Signed-Request Replay with Arbitrary Body

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

AnyCable is a realtime server for reliable two-way communication that supports any backend. Prior to 1.6.15, the Pusher-compatible REST API in pusher/http.go includes the caller-supplied body_md5 value in the HMAC input but does not calculate the digest of the received request body or compare it with the signed value. An attacker who obtains a legitimate signed POST request can retain its query parameters and auth_signature while replacing the body, causing Handler and handleEvents to accept and broadcast attacker-selected event content. The absence of an auth_timestamp freshness check also allows the captured signature to be replayed indefinitely. This can forge server-side events, modify application state, or deliver attacker-controlled messages to WebSocket clients within the signed request's application context. This issue is fixed in version 1.6.15.

Source published

18 Sep 2026 16:47:37 UTC

Source modified

18 Sep 2026 17:07:38 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

AnyCable is a realtime server for reliable two-way communication that supports any backend. Prior to 1.6.15, the Pusher-compatible REST API in pusher/http.go includes the caller-supplied body_md5 value in the HMAC input but does not calculate the digest of the received request body or compare it with the signed value. An attacker who obtains a legitimate signed POST request can retain its query parameters and auth_signature while replacing the body, causing Handler and handleEvents to accept and broadcast attacker-selected event content. The absence of an auth_timestamp freshness check also allows the captured signature to be replayed indefinitely. This can forge server-side events, modify application state, or deliver attacker-controlled messages to WebSocket clients within the signed request's application context. This issue is fixed in version 1.6.15.

Source published

Sep 18, 2026, 4:47:37 PM (timezone not stated)

Source modified

Sep 18, 2026, 5:07:38 PM (timezone not stated)

Observed here

11 Nov 2026 15:06:06 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

AnyCable is a realtime server for reliable two-way communication that supports any backend. Prior to 1.6.15, the Pusher-compatible REST API in pusher/http.go includes the caller-supplied body_md5 value in the HMAC input but does not calculate the digest of the received request body or compare it with the signed value. An attacker who obtains a legitimate signed POST request can retain its query parameters and auth_signature while replacing the body, causing Handler and handleEvents to accept and broadcast attacker-selected event content. The absence of an auth_timestamp freshness check also allows the captured signature to be replayed indefinitely. This can forge server-side events, modify application state, or deliver attacker-controlled messages to WebSocket clients within the signed request's application context. This issue is fixed in version 1.6.15.

Source published

18 Sep 2026 17:16:59 UTC

Source modified

24 Sep 2026 21:25:27 UTC

Observed here

25 Oct 2026 15:18:45 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

### Summary The Pusher-compatible REST API includes `body_md5` in the HMAC signature string but never computes or verifies the MD5 of the received HTTP body, allowing anyone who observes a signed request to replay it with an entirely different body. ### Details In `pusher/http.go`, the `Handler` function extracts `body_md5` from the URL query string (line 169) and includes it verbatim in `stringToSign` (line 175). It then verifies `HMAC(stringToSign, secret) == auth_signature`. After verification succeeds, `handleEvents` reads and parses `r.Body` (lines 201-212) without ever computing `md5(body)` and comparing it against the `body_md5` that was signed. The Pusher protocol specification explicitly requires the server to verify this digest to prevent body-substitution attacks. There is also no `auth_timestamp` staleness check, so replays are valid indefinitely. ### PoC 1. Capture a legitimate signed POST to `/apps/<app_id>/events?auth_key=K&auth_timestamp=T&auth_version=1.0&body_md5=LEGIT_MD5&auth_signature=SIG` carrying body `{"name":"safe-event","channel":"ch","data":"..."}` (e.g., from TLS-terminating load-balancer logs). 2. Send a new request with the same query string parameters but a different body: `{"name":"injected-event","channel":"admin","data":"malicious-payload"}` 3. The server accepts the request (HMAC over `stringToSign` matches the original) and broadcasts the injected event to all subscribers of `admin`. ### Impact An attacker who can read any single signed Pusher API request (from logs, a shared proxy, or a network tap) can broadcast arbitrary events to any channel indefinitely, potentially forging server-side events, corrupting application state, or delivering phishing messages to WebSocket clients. ### Fix After reading `r.Body`, compute `hex(md5(body))` and compare it to the `body_md5` query parameter using a constant-time comparison before proceeding. Additionally, reject requests whose `auth_timestamp` is more than 600 seconds from the current time.

Source published

18 Sep 2026 17:16:25 UTC

Source modified

28 Sep 2026 17:10:52 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Publisher rating · MODERATE

AnyCable: Pusher REST API Does Not Verify Request Body MD5 Enabling Signed-Request Replay with Arbitrary Body in github.com/anycable/anycable-go. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/anycable/anycable-go before v1.6.15.

Source published

28 Sep 2026 16:43:40 UTC

Source modified

28 Sep 2026 17:00:16 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.