EUVD-2026-63660
GHSA-fv6j-9p8m-c3wr
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Fully network-exploitable with no authentication, no complexity, and no user interaction; only availability is affected as no data is exposed or modified.
Primary rating from Vendor (6b3ad84c-e1a6-4bf7-a703-f496b71e49db).
CVSS VectorVendor: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4DescriptionCVE.org
Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows an unauthenticated remote attacker to pin an unbounded number of HTTP/2 stream processes indefinitely via connection-level flow control. When a stream's response body outruns the HTTP/2 connection-level send window (default 65,535 bytes, shared across all streams on the connection), Bandit.HTTP2.Connection queues the remaining bytes and a reply closure in pending_sends and the stream process blocks forever inside a synchronous call to the connection process. Nothing bounds that wait and nothing purges the queue: a client RST_STREAM for the blocked stream is delivered to its mailbox but never read while it is stuck inside the call, so cancelling frees nothing, and periodic PING frames keep the transport-level read timeout from ever firing. The equivalent block on the stream-level send window is already bounded at 15 seconds; the connection-level path had no such bound.
Each stalled stream pins its process, Plug state, and any resource the Plug holds across the blocked write, such as a pooled upstream connection in a reverse-proxy Plug. The attacker chooses any endpoint whose response exceeds the connection window (common for most non-trivial payloads), grants a generous stream-level window so only the connection window limits it, and keeps the connection alive with periodic PINGs; the primitive is repeatable across streams and connections at the cost of one idle socket each.
This issue affects bandit: from 0.3.4 before 1.12.5.
AnalysisAI
Denial-of-service in Bandit (Elixir HTTP server) versions 0.3.4 through 1.12.4 allows unauthenticated remote attackers to pin an unbounded number of HTTP/2 stream processes indefinitely by exploiting the absence of any timeout on the connection-level HTTP/2 send window queue. When a response body exceeds the default 65,535-byte connection window, the stream process blocks forever inside a synchronous GenServer call, and neither RST_STREAM frames nor periodic PING keepalives free the stalled resources in vulnerable versions - the attacker can keep the connection alive with PINGs specifically to defeat the transport read timeout. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | HTTP/2 must be negotiated on the connection (TLS with ALPN 'h2' or h2c cleartext where enabled). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VA:H) accurately captures the threat profile: fully network-exploitable with no prerequisites, no authentication, and no user interaction, resulting in high availability impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker opens an HTTP/2 connection to any Bandit-served endpoint that returns a response body larger than 65,535 bytes - a threshold met by most non-trivial API responses, file downloads, or proxied upstream replies - and advertises a permissively large stream-level flow-control window so the connection-level window becomes the sole bottleneck. Once the stream process is blocked in its synchronous GenServer call, the attacker sends periodic HTTP/2 PING frames to prevent the transport read timeout from firing and issues RST_STREAM (which is silently ignored in vulnerable versions), then repeats this pattern across additional streams and connections, each pinning an Elixir process and any pooled resources it holds until the server is resource-exhausted. |
| Remediation | The primary fix is to upgrade Bandit to version 1.12.5, which resolves the vulnerability by adding a 15-second expiry (@pending_send_timeout 15_000) to all connection-level pending sends, introducing expire_pending_sends/1 (triggered on every inbound frame including PING keepalives) to evict stalled sends, and wiring purge_pending_send/2 into RST_STREAM and stream process exit handling so stream cancellation actually frees queued resources. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: identify all systems running Bandit 0.3.4-1.12.4 using software bill of materials, dependency scanning, and container registry analysis; implement emergency rate limiting on load balancers or reverse proxies to restrict concurrent HTTP/2 streams to 10-50 per source IP to bound resource exhaustion. …
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Same technique Denial Of Service
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External POC / Exploit Code
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