GHSA-G586-CCQF-7X4R

Vulnerability from github – Published: 2026-07-09 23:19 – Updated: 2026-07-09 23:19
VLAI
Summary
mint: Unbounded streams map growth via PUSH_PROMISE without follow-up HEADERS
Details

Summary

Mint's HTTP/2 client accepts PUSH_PROMISE frames from any server it connects to and inserts every promised stream into a per-connection map without consulting max_concurrent_streams. A malicious or compromised HTTP/2 server can flood the client with PUSH_PROMISE frames and withhold the matching response HEADERS, pinning one map entry per frame indefinitely until the client process runs out of memory.

Details

'Elixir.Mint.HTTP2':handle_push_promise/3 in lib/mint/http2.ex dispatches every inbound PUSH_PROMISE frame to 'Elixir.Mint.HTTP2':decode_push_promise_headers_and_add_response/5, which inserts a :reserved_remote entry into conn.streams for the promised ID. The only validation applied is that the promised ID is even and not already present; client_settings.max_concurrent_streams is not consulted at promise time.

The concurrency cap is only checked when the response HEADERS for the promised stream arrive. A server that emits PUSH_PROMISE frames and never sends the matching HEADERS never trips that check, and the existing tally counts only streams in open states, not :reserved_remote entries.

HTTP/2 server push is accepted by default (client_settings.enable_push defaults to true), so no application opt-in is required. A single long-lived HTTP/2 connection to a hostile server lets it pin one conn.streams entry per PUSH_PROMISE frame, with no upper bound.

PoC

  1. Stand up a raw TCP HTTP/2 server that completes the handshake and ACKs the client's SETTINGS.
  2. Wait for the client's request HEADERS and capture its odd stream ID.
  3. Send a flood of PUSH_PROMISE frames (flags = END_HEADERS) associated with the captured stream, each promising a fresh even stream ID and carrying a minimal HPACK-encoded header block.
  4. Never send the matching response HEADERS for any of the promised IDs.
  5. The client's conn.streams map grows by one entry per PUSH_PROMISE frame (~148 bytes/entry); memory grows linearly and the BEAM process eventually crashes with OOM.

Impact

Remote, unauthenticated denial-of-service against any process using Mint as an HTTP/2 client against an untrusted or attacker-influenced server. Server push is on by default, so no application code change can prevent it short of disabling push or upgrading. Affected populations include outbound HTTP/2 clients in web backends, webhook delivery systems, scrapers, federated and proxy components, and any service that follows redirects to third-party HTTP/2 origins.

Workarounds

Disable HTTP/2 server push on connections to untrusted servers by passing client_settings: [enable_push: false] to 'Elixir.Mint.HTTP':connect/4. Mint will then reject any inbound PUSH_PROMISE frame with a PROTOCOL_ERROR before the vulnerable code path is reached.

Resources

  • Introduction commit: https://github.com/elixir-mint/mint/commit/65c6394d05a1b8aa4a7461708c3aa173e8d7a5cf
  • Patch commit: https://github.com/elixir-mint/mint/commit/70b97b6a5209fb288b0e04d8e657dda26c59de67
Severity
8.2 (High)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "mint"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.2.0"
            },
            {
              "fixed": "1.9.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48862"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-09T23:19:29Z",
    "nvd_published_at": "2026-06-02T16:16:44Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nMint\u0027s HTTP/2 client accepts `PUSH_PROMISE` frames from any server it connects to and inserts every promised stream into a per-connection map without consulting `max_concurrent_streams`. A malicious or compromised HTTP/2 server can flood the client with `PUSH_PROMISE` frames and withhold the matching response `HEADERS`, pinning one map entry per frame indefinitely until the client process runs out of memory.\n\n### Details\n\n`\u0027Elixir.Mint.HTTP2\u0027:handle_push_promise/3` in `lib/mint/http2.ex` dispatches every inbound `PUSH_PROMISE` frame to `\u0027Elixir.Mint.HTTP2\u0027:decode_push_promise_headers_and_add_response/5`, which inserts a `:reserved_remote` entry into `conn.streams` for the promised ID. The only validation applied is that the promised ID is even and not already present; `client_settings.max_concurrent_streams` is not consulted at promise time.\n\nThe concurrency cap is only checked when the response `HEADERS` for the promised stream arrive. A server that emits `PUSH_PROMISE` frames and never sends the matching `HEADERS` never trips that check, and the existing tally counts only streams in open states, not `:reserved_remote` entries.\n\nHTTP/2 server push is accepted by default (`client_settings.enable_push` defaults to `true`), so no application opt-in is required. A single long-lived HTTP/2 connection to a hostile server lets it pin one `conn.streams` entry per `PUSH_PROMISE` frame, with no upper bound.\n\n### PoC\n\n1. Stand up a raw TCP HTTP/2 server that completes the handshake and ACKs the client\u0027s `SETTINGS`.\n2. Wait for the client\u0027s request `HEADERS` and capture its odd stream ID.\n3. Send a flood of `PUSH_PROMISE` frames (`flags = END_HEADERS`) associated with the captured stream, each promising a fresh even stream ID and carrying a minimal HPACK-encoded header block.\n4. Never send the matching response `HEADERS` for any of the promised IDs.\n5. The client\u0027s `conn.streams` map grows by one entry per `PUSH_PROMISE` frame (~148 bytes/entry); memory grows linearly and the BEAM process eventually crashes with OOM.\n\n### Impact\n\nRemote, unauthenticated denial-of-service against any process using Mint as an HTTP/2 client against an untrusted or attacker-influenced server. Server push is on by default, so no application code change can prevent it short of disabling push or upgrading. Affected populations include outbound HTTP/2 clients in web backends, webhook delivery systems, scrapers, federated and proxy components, and any service that follows redirects to third-party HTTP/2 origins.\n\n## Workarounds\n\nDisable HTTP/2 server push on connections to untrusted servers by passing `client_settings: [enable_push: false]` to `\u0027Elixir.Mint.HTTP\u0027:connect/4`. Mint will then reject any inbound `PUSH_PROMISE` frame with a `PROTOCOL_ERROR` before the vulnerable code path is reached.\n\n## Resources\n\n* Introduction commit: https://github.com/elixir-mint/mint/commit/65c6394d05a1b8aa4a7461708c3aa173e8d7a5cf\n* Patch commit: https://github.com/elixir-mint/mint/commit/70b97b6a5209fb288b0e04d8e657dda26c59de67",
  "id": "GHSA-g586-ccqf-7x4r",
  "modified": "2026-07-09T23:19:29Z",
  "published": "2026-07-09T23:19:29Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/elixir-mint/mint/security/advisories/GHSA-g586-ccqf-7x4r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48862"
    },
    {
      "type": "WEB",
      "url": "https://github.com/elixir-mint/mint/commit/70b97b6a5209fb288b0e04d8e657dda26c59de67"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-48862.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/elixir-mint/mint"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-48862"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "mint: Unbounded streams map growth via PUSH_PROMISE without follow-up HEADERS"
}



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