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Response snapshot Oct 26, 2026, 23:38 UTC

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VulnerabilityCVE-2026-112396

Pillow: Heap use-after-free when encoding TIFF to an in-memory buffer

- `src/libImaging/TiffDecode.c:1041-1046` Teardown then calls `ImagingLibTiffEncodeCleanup`, which runs `TIFFClose(tiff)` because `tiff` is still set:

Published Updated

At a glance

Exploited
Not known
Severity
5.9 Medium (CVSS 3.1)
Chance of exploitation
0.6% 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-4rr5-89j8-mwwm (opens a new tab)

What happened

### Summary Saving an image as TIFF to an in-memory buffer can trigger a heap use-after-free if libtiff rejects a tag at encode time. When `TIFFWriteScanline` fails, the encoder frees its output buffer but leaves the libtiff handle open. Later, when the encoder object is torn down, `TIFFClose` flushes buffered bytes through the write callback and writes into the freed buffer.

An application that re-encodes attacker-influenced images to TIFF in memory can be crashed and is a candidate for remote code execution.

### Details The failure path in `ImagingLibTiffEncode` frees `clientstate->data` for the in-memory case but does not close the TIFF or null `clientstate->tiff` (the file-descriptor branch just above it does set `tiff = NULL`):

- `src/libImaging/TiffDecode.c:1041-1046`

Continue reading

Teardown then calls `ImagingLibTiffEncodeCleanup`, which runs `TIFFClose(tiff)` because `tiff` is still set:

- `src/encode.c:99-101` - `src/libImaging/TiffDecode.c:955`

`TIFFClose` flushes through `_tiffWriteProc`, which reallocs and memcpys into the freed `state->data`:

- `src/libImaging/TiffDecode.c:103-115`

The Predictor tag is a convenient trigger: the floating-point predictor (value 3) is invalid for integer sample data, so libtiff aborts the write.

### PoC ```python import io from PIL import Image

# In-memory TIFF re-encode. libtiff rejects Predictor=3 (floating point) on integer # data, so TIFFWriteScanline fails. The encoder frees clientstate->data but leaves the # TIFF open; cleanup's TIFFClose then writes through the callback into the freed buffer. im = Image.new("L", (64, 64)) buf = io.BytesIO() im.save(buf, format="TIFF", compression="tiff_lzw", tiffinfo={317: 3}) # 317 = Predictor ```

Run it: ``` $ python 01_poc.py PredictorSetup: Floating point "Predictor" not supported with 1 data format. OSError: encoder error -2 when writing image file Segmentation fault (core dumped) ```

Observed on a source build of commit `3e2ab96` with libtiff. The process aborts during cleanup after the encoder error. Depending on heap state the same run sometimes reports `corrupted double-linked list` instead of a segfault; both are the same write into freed memory.

Under AddressSanitizer (build with `-fsanitize=address`), relevant frames: ``` ==ERROR: AddressSanitizer: heap-use-after-free on address 0x7ef737b48804 WRITE of size 4 at 0x7ef737b48804 thread T0 #1 _tiffWriteProc src/libImaging/TiffDecode.c:115 #3 TIFFFlush libtiff.so.6 #5 TIFFClose libtiff.so.6 #6 ImagingLibTiffEncodeCleanup src/libImaging/TiffDecode.c:955 #7 _dealloc src/encode.

c:100 freed by thread T0 here: #1 ImagingLibTiffEncode src/libImaging/TiffDecode.c:1045 #2 _encode src/encode.c:139 previously allocated by thread T0 here: #1 ImagingLibTiffEncodeInit src/libImaging/TiffDecode.c:863 #2 PyImaging_LibTiffEncoderNew src/encode.c:757 SUMMARY: AddressSanitizer: heap-use-after-free src/libImaging/TiffDecode.

c:115 in _tiffWriteProc ``` The buffer allocated in `ImagingLibTiffEncodeInit` is freed in `ImagingLibTiffEncode`, then written by `_tiffWriteProc` during the `TIFFClose` flush that runs from the encoder's `_dealloc`.

### Impact Use-after-free in a C extension. Affects any service that converts or thumbnails untrusted images to TIFF in memory (a `BytesIO` or other non-seekable target). Result is a crash and possible memory corruption leading to code execution.

Affected package ranges reported by GitHub: pillow: >= 11.3.0, < 13.0.0

Scores and how they were measured

CVSS base severity

5.9

Version 3.1As of

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

Measurement source (opens a new tab)

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

EPSS probability

0.6%

Scored Percentile 47.8%

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-4rr5-89j8-mwwm (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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, 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-4rr5-89j8-mwwm, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-112396 (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

    Vendor advisory (via NVD references) (opens a new tab)

    The vendor advisory referenced by the CVE record, for affected versions and fixes.

    Published Date not suppliedChecked

  14. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  15. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  16. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  17. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-112396, 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 26). Pillow: Heap use-after-free when encoding TIFF to an in-memory buffer (CVE-2026-112396). https://kevwire.com/record/CVE-2026-112396

MLA

"Pillow: Heap use-after-free when encoding TIFF to an in-memory buffer (CVE-2026-112396)." KEVWire, 26 Oct. 2026, kevwire.com/record/CVE-2026-112396.

Chicago

KEVWire. "Pillow: Heap use-after-free when encoding TIFF to an in-memory buffer (CVE-2026-112396)." Last modified October 26, 2026. https://kevwire.com/record/CVE-2026-112396.

Evidence summary (plain text)

Pillow: Heap use-after-free when encoding TIFF to an in-memory buffer (Oct 21, 2026).
- `src/libImaging/TiffDecode.c:1041-1046`

Teardown then calls `ImagingLibTiffEncodeCleanup`, which runs `TIFFClose(tiff)` because `tiff` is still set:
CVSS 5.9 (version 3.1; evidence as of Oct 26, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-112396).
EPSS 0.6% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-112396&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-4rr5-89j8-mwwm: https://github.com/advisories/GHSA-4rr5-89j8-mwwm
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=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
NVD CVE-2026-112396: https://nvd.nist.gov/vuln/detail/CVE-2026-112396
Vendor advisory (via NVD references): https://github.com/python-pillow/Pillow/security/advisories/GHSA-4rr5-89j8-mwwm
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T20:37:18.143Z&lastModEndDate=2026-10-26T22:10:56.995Z&resultsPerPage=500&startIndex=2000
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T20:05:59.720Z&lastModEndDate=2026-10-26T21:35:56.549Z&resultsPerPage=500&startIndex=2000
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T19:31:27.927Z&lastModEndDate=2026-10-26T21:05:56.246Z&resultsPerPage=500&startIndex=0
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-112396&date=2026-10-26
Record ID: CVE-2026-112396.
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 26, 2026, 19:40 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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