Vulnerability · Published Jun 2, 2026 · Assigned by EEF
CVE-2026-48862Unbounded conn.streams growth in Mint HTTP/2 client via unenforced PUSH_PROMISE concurrency
High 8.2
In plain English
A high-severity resource allocation without limits in mint from elixir-mint. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities).
Official description
Allocation of Resources Without Limits or Throttling vulnerability in elixir-mint Mint allows attacker-controlled HTTP/2 servers to exhaust memory in a Mint client via PUSH_PROMISE flooding. In lib/mint/http2.ex, Mint.HTTP2.decode_push_promise_headers_and_add_response/5 inserts a :reserved_remote entry into conn.streams for every promised stream ID. The neighbouring Mint.HTTP2.assert_valid_promised_stream_id/2 only verifies 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, so a server that emits PUSH_PROMISE frames and withholds the matching HEADERS never trips that check. HTTP/2 server push is accepted by default (client_settings.enable_push defaults to true). A single long-lived HTTP/2 connection to a hostile server lets that server pin one conn.streams entry per PUSH_PROMISE frame it sends, with no upper bound, until the client process runs out of memory. This issue affects mint: from 0.2.0 before 1.9.0.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| elixir-mint | mint | 0.2.0 – before 1.9.0 |
| elixir-mint | mint | 65c6394d05a1b8aa4a7461708c3aa173e8d7a5cf – before 70b97b6a5209fb288b0e04d8e657dda26c59de67 |
Weakness: CWE-770 · Vector: 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