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Response snapshot Oct 27, 2026, 07:27 UTC

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VulnerabilityCVE-2026-113656

ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS

**Summary** The form submission endpoint runs `multer({ dest: os.tmpdir() }).any()` before authentication, API-key, CSRF-equivalent, or form-existence logic, with no size/count/rate limits.

Published Updated

At a glance

Exploited
Not known
Severity
5.3 Medium (CVSS 3.1)
Chance of exploitation
0.5% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: @apostrophecms/form: 1.5.5. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-89mh-mm8c-mv7f (opens a new tab)

What happened

**Summary** The form submission endpoint runs `multer({ dest: os.tmpdir() }).any()` before authentication, API-key, CSRF-equivalent, or form-existence logic, with no size/count/rate limits. Unauthenticated users can stream unbounded bodies to disk per request; cleanup occurs only after the full body is received.

**Details** `packages/form/index.js` `apiRoutes.post.submit` (L274–296): `[ multer({ dest: os.tmpdir() }).any(), self.normalizeFiles, async function (req) { try { submitForm } finally { unlink files } } ]`. No `limits`, no rate limiting, no pre-validation. "CSRF" is a fixed-value double-submit cookie (`vulnlab.csrf=csrf`, set on any GET, express/index.js L694–703) — trivially obtainable anonymously.

**PoC** ``` $ curl -s -c csrfjar.cookies http://localhost:3100/ # get vulnlab.csrf=csrf (any GET) $ df -P /tmp # before: used=1105212 $ curl -b csrfjar.cookies -X POST http://localhost:3100/api/v1/@apostrophecms/form/submit \ -F "file=@/tmp/opencode/big.bin;type=application/octet-stream" & DURING transfer: used=1148668 still transferring: used=1226936 # +121MB mid-transfer on disk http=500 time=1.

78s sent=209715411B # generic error AFTER full staging # Anonymous, zero credentials. 200MB written to /tmp pre-validation. ```

Continue reading

**Impact** Any unauthenticated client can force the server to persist entire request bodies to the temp filesystem and CPU-decode them; parallel requests exhaust disk `/tmp` (process/host crash) and saturate the event loop — a trivial remote DoS. Aborted transfers risk orphaning staged files (no `req.aborted` cleanup).

**Remediation** — Set multer `limits` (fileSize, fields, parts, fieldSize); perform auth/role/existence checks before the multer mount or inside the checked handler; unlink staged files on first read and on `req.aborted`/error; add per-IP rate limiting.

Affected package ranges reported by GitHub: @apostrophecms/form: < 1.5.5

Scores and how they were measured

CVSS base severity

5.3

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.5%

Scored Percentile 39.8%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-89mh-mm8c-mv7f (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-89mh-mm8c-mv7f, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-89mh-mm8c-mv7f, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-89mh-mm8c-mv7f, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-113656, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 20). ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS (CVE-2026-113656). https://kevwire.com/record/CVE-2026-113656

MLA

"ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS (CVE-2026-113656)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-113656.

Chicago

KEVWire. "ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS (CVE-2026-113656)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-113656.

Evidence summary (plain text)

ApostropheCMS: Unauthenticated unbounded multipart upload → disk-exhaustion DoS (Oct 20, 2026).
**Summary**
The form submission endpoint runs `multer({ dest: os.tmpdir() }).any()` before authentication, API-key, CSRF-equivalent, or form-existence logic, with no size/count/rate limits. Unauthenticated users can stream unbounded bodies to disk per request; cleanup occurs only after the full body is received.

**Details**
`packages/form/index.js` `apiRoutes.post.submit` (L274–296): `[ multer({ dest: os.tmpdir() }).any(), self.normalizeFiles, async function (req) { try { submitForm } finally { unlink files } } ]`. No `limits`, no rate limiting, no pre-validation. "CSRF" is a fixed-value double-submit cookie (`vulnlab.csrf=csrf`, set on any GET, express/index.js L694–703) — trivially obtainable anonymously.
CVSS 5.3 (version 3.1; evidence as of Oct 20, 2026; https://github.com/advisories/GHSA-89mh-mm8c-mv7f).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113656&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-89mh-mm8c-mv7f: https://github.com/advisories/GHSA-89mh-mm8c-mv7f
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDo0NTowN1rOAAfvzQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDozMDoyNlrOAAfvxw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDowMzo1N1rOAAfvxQ%3D%3D
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-113656&date=2026-10-26
Record ID: CVE-2026-113656.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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