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Response snapshot Oct 27, 2026, 00:58 UTC

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VulnerabilityCVE-2026-112897

Pillow: TiffDecode returns uninitialized memory as pixels for short JPEG strips

``` ============================================================================ TiffDecode returns uninitialized memory as pixels for short JPEG strips Location: src/libImaging/TiffDecode.

Published Updated

At a glance

Exploited
Not known
Severity
8.7 High (CVSS 4.0)
Chance of exploitation
0.5% 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-q45j-58j2-45rg (opens a new tab)

What happened

``` ============================================================================ TiffDecode returns uninitialized memory as pixels for short JPEG strips Location: src/libImaging/TiffDecode.c:554 in _decodeStrip() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

Pillow hands back leftover process memory as image pixels when it opens a small crafted TIFF file. Anyone who can get an application to open their image, and can see something produced from its pixels (a thumbnail, a preview, a converted copy), can read heap memory that the process had previously used and freed.

This works in the default configuration: opening and loading the 478-byte file succeeds with no error or warning, and every row below the first eight holds stale memory instead of picture content.

The bug is in `_decodeStrip()` in `src/libImaging/TiffDecode.c`, and `_decodeTile()` has the same shape. The function `realloc()`s `state->buffer` to `TIFFStripSize()` bytes without initialising it and calls `TIFFReadEncodedStrip()`. Whenever that call does not return -1, it copies all `RowsPerStrip` rows of the buffer into the image.

Continue reading

libtiff's JPEG codec only warns when the JPEG embedded in a strip has fewer rows than the strip, and Pillow silences libtiff warnings. The codec decodes the rows that exist and still returns the full strip size, so the untouched remainder is copied out as pixels. libtiff's Group 4 fax codec behaves the same way for a stream that ends early.

The attached reproducer builds a 256×256 TIFF whose single strip or tile is a 256×8 JPEG. Before loading it, the script frees buffers filled with `b"LEAK"`. It then finds 15,872 copies of `LEAK` in rows 8–255 of the decoded image (the same freed chunk was reused in 500 of 500 runs). Under glibc's `MALLOC_PERTURB_`, those rows are entirely the allocator's fill byte. A well-formed control file decodes correctly in both cases.

This is a read of uninitialised heap memory, not memory corruption. Each strip can disclose up to width × `RowsPerStrip` bytes, and what comes back depends on the allocator's state at the time. The strip path was introduced in e91b851fdc1c ("Add reading old-JPEG compressed TIFFs", first released in Pillow 6.0.0). The tile path has had the same pattern since f0436a4ddc95 (Pillow 5.3.0).

## Details

`src/libImaging/TiffDecode.c` decodes compressed TIFFs through libtiff into a strip (or tile) buffer that it `realloc()`s to `TIFFStripSize()` bytes and never initialises, and then copies all `RowsPerStrip` rows of that buffer into the image whenever `TIFFReadEncodedStrip()` does not return -1.

libtiff's JPEG codec does not fail when the JPEG stream inside a strip has fewer rows than the strip: it decodes the rows that exist and returns the full strip size. The rows it did not write are whatever the heap held before, and Pillow returns them as pixels.

A 478-byte file shows it: a classic little-endian TIFF, 256×256, `BitsPerSample=8`, `Compression=7`, `PhotometricInterpretation=1`, `RowsPerStrip=256`, one strip whose data is a baseline JPEG of 256×**8** pixels (as written by `Image.new("L",(256,8),200).save(…,"JPEG")`). `Image.open(BytesIO(data)).load()` succeeds with default settings (compressed TIFFs always take the libtiff path).

Rows 0–7 of the result are the JPEG content (value 200); the remaining 63488 bytes of `im.tobytes()` are heap garbage: run under glibc's `MALLOC_PERTURB_=1` they are all `0xFE`, under `MALLOC_PERTURB_=170` all `0x55` (the fresh-`malloc` fill byte), and in a process that has just freed buffers containing `b"LEAK"` they contain 15872 copies of `LEAK`.

Feeding the same file to libtiff 4.5.0 directly confirms the library side: `TIFFReadEncodedStrip(t, 0, buf, 65536)` prints `JPEGPreDecode: Warning, Improper JPEG strip/tile size, expected 256x256, got 256x8.`, returns 65536, and leaves 63488 of the 65536 buffer bytes untouched. Pillow installs `TIFFSetWarningHandler(NULL)` (`TiffDecode.c:682`), so the warning is not visible either.

The strip path:

```c // src/libImaging/TiffDecode.c:552 /* realloc to fit whole strip */ /* malloc check above */ new_data = realloc(state->buffer, state->bytes); // state->bytes = TIFFStripSize() … state->buffer = new_data;

for (; state->y ysize; state->y += rows_per_strip) { … if (TIFFReadEncodedStrip( tiff, TIFFComputeStrip(tiff, state->y, plane), (tdata_t)state->buffer, strip_size ) == -1) { … return -1; } … // iterate over each row in the strip and stuff data into image for (strip_row = 0; strip_row ysize - state->y); strip_row++) { … shuffler( (UINT8 *)im->image[state->y + state->yoff + strip_row] + state->xoff * im->pixelsize, state->buffer + strip_row * row_byte_size, state->xsize ); ```

`state->buffer` arrives here as the one-row `calloc` made by `decode.c:230` (`(bits*xsize+7)/8` = 256 bytes for the example). The `realloc` to 65536 bytes hands back a different, uninitialised chunk; nothing zeroes it.

`TIFFReadEncodedStrip()` returns the nominal strip size on success, not the number of rows produced, and the only check is `== -1`, so the row loop unconditionally copies 256 rows × 256 bytes into `im->image` (which itself is zeroed by `core.new`, so the garbage provably comes from `state->buffer`). `_decodeTile()` has the same shape (`TiffDecode.

c:448` `realloc` to `TIFFTileSize()`, then `tile_length` rows copied after each `TIFFReadTile()` at 460–488).

For a well-formed file the JPEG inside the strip is 256×256, libtiff fills all 65536 bytes and the copy is correct. The malicious file differs only in the SOF height of the embedded JPEG; libtiff treats "JPEG smaller than strip" as a warning, clamps the row count to the JPEG height, and reports success.

JPEG is not the only libtiff codec that succeeds on a short strip. `Fax4Decode` (`Compression=4`) returns success for a T.6 stream that ends early: a 133-byte 512×256 1-bit TIFF whose strip is the Group 4 stream of a 512×16 im

Affected package ranges reported by GitHub: Pillow: >= 5.3.0, < 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:H/VI:N/VA:N/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

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 43.4%

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-q45j-58j2-45rg (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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, 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-q45j-58j2-45rg, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-112897 (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-2026-112897, 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 22). Pillow: TiffDecode returns uninitialized memory as pixels for short JPEG strips (CVE-2026-112897). https://kevwire.com/record/CVE-2026-112897

MLA

"Pillow: TiffDecode returns uninitialized memory as pixels for short JPEG strips (CVE-2026-112897)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-112897.

Chicago

KEVWire. "Pillow: TiffDecode returns uninitialized memory as pixels for short JPEG strips (CVE-2026-112897)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-112897.

Evidence summary (plain text)

Pillow: TiffDecode returns uninitialized memory as pixels for short JPEG strips (Oct 20, 2026).
```
============================================================================
TiffDecode returns uninitialized memory as pixels for short JPEG strips
Location: src/libImaging/TiffDecode.c:554 in _decodeStrip()
Commit: a707c6b21c313880d0771e54965d142dd42358b6
============================================================================
```

Pillow hands back leftover process memory as image pixels when it opens a small crafted TIFF file. Anyone who can get an application to open their image, and can see something produced from its pixels (a thumbnail, a preview, a converted copy), can read heap memory that the process had previously used and freed. This works in the default configuration: opening and loading the 478-byte file succeeds with no error or warning, and every row below the first eight holds stale memory instead of picture content.
CVSS 8.7 (version 4.0; evidence as of Oct 22, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-112897).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-112897&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-q45j-58j2-45rg: https://github.com/advisories/GHSA-q45j-58j2-45rg
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-2026-112897: https://nvd.nist.gov/vuln/detail/CVE-2026-112897
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-2026-112897&date=2026-10-26
Record ID: CVE-2026-112897.
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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