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Response snapshot Oct 27, 2026, 05:48 UTC

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VulnerabilityCVE-2026-96778

Pillow: Heap buffer overflow writing JPEG comment after ICC profile fills buffer

``` ============================================================================ Heap buffer overflow writing JPEG comment after ICC profile fills buffer Location: src/libImaging/JpegEncode.

Published Updated

At a glance

Exploited
Not known
Severity
7.7 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-g7cr-3p24-7wf7 (opens a new tab)

What happened

``` ============================================================================ Heap buffer overflow writing JPEG comment after ICC profile fills buffer Location: src/libImaging/JpegEncode.c:330 in ImagingJpegEncode() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ```

A heap buffer overflow in Pillow's JPEG encoder lets anyone who can supply an image write up to 64 KB of bytes they choose, followed by the rest of the compressed image, past the end of a 64 KB heap buffer. The target is any application that re-saves the image as JPEG while keeping its colour profile. The reliable result is that the Python process is killed outright rather than raising an exception.

Because the overwritten memory sits directly in front of function pointers that the encoder calls next, this could allow code execution, though the attached reproducer demonstrates only the crash.

The bug is in `ImagingJpegEncode()` in `src/libImaging/JpegEncode.c`. State 4 (line 330) calls `jpeg_write_marker()` for the COM comment marker without checking that the output buffer has room. Meanwhile, `JpegImagePlugin._save()` sizes that buffer from the EXIF and ICC/XMP data only and reserves nothing for the comment.

Continue reading

When a 65498-byte ICC profile fills the 65536-byte buffer exactly, libjpeg's `emit_byte()` stores one byte past the end and then decrements `free_in_buffer` from 0. The `size_t` counter wraps, so the marker, the comment and the entire compressed image are written out of bounds.

Triggering it takes only a valid JPEG (or PNG) carrying that profile and any comment, passed through `Image.open()` and then `im.save(..., "JPEG", icc_profile=im.info.get("icc_profile"))`. That is the documented way to preserve colour. The comment is forwarded from `im.info` automatically, and no non-default setting is involved.

The attached reproducer re-saves such a file on the stock build, and the process dies with SIGSEGV. An identical file without the comment saves normally. An ASan build of Pillow will not flag this, because the stray writes happen inside the system libjpeg-turbo. Valgrind does report it, as an invalid write immediately after the 65569-byte allocation.

The unguarded call was introduced in e50ae85ea406 ("Use jpeg_write_marker to write comment", 2022-12-05) and first shipped in 9.4.0.

## Details

`ImagingJpegEncode()` (`src/libImaging/JpegEncode.c`) is a resumable state machine that fills a caller-supplied output buffer of `bytes` bytes and returns when it is full. State 4 writes the JPEG COM marker with `jpeg_write_marker()` without first checking that the buffer has any room left.

When the preceding state 3 — the verbatim copy of the "extra" APP segments (ICC profile / XMP) — ends exactly at the last byte of the buffer, `jpeg_write_marker()` is entered with `free_in_buffer == 0`.

libjpeg's `emit_byte()` stores the byte first and tests `--free_in_buffer == 0` afterwards, so the `size_t` counter wraps to 2^64-1 instead of triggering the "buffer full" path, and the 4-byte marker header, the whole comment, and then (state 5) the DQT/SOF/DHT/SOS headers and the entire entropy-coded image are written linearly past the end of the 65536-byte heap buffer allocated in `src/encode.c`.

A JPEG laid out as

``` FFD8 SOI FFE2 "ICC_PROFILE\0" 01 01 -> im.info["icc_profile"] FFFE -> im.info["comment"]

```

opened with `Image.open()` and re-saved with the usual colour-profile-preserving call

```python im.save(out, "JPEG", icc_profile=im.info.get("icc_profile")) ```

kills the Python process on the stock build at this commit: glibc aborts with `realloc(): invalid next size` / `corrupted size vs. prev_size`, or the process takes SIGSEGV inside `jpeg_write_marker`/`jpeg_write_scanlines`. Stopping at `JpegEncode.

c:330` in gdb shows `next_output_byte - buf == 65536`, `free_in_buffer == 0`, `comment_size == 65533` before the call, and `next_output_byte - buf == 131073`, `free_in_buffer == 18446744073709486079` after it — 65537 bytes already written beyond a 65536-byte buffer before a single scanline has been encoded.

An ASan build of Pillow does not flag this, because the out-of-bounds stores happen inside the (uninstrumented) system libjpeg-turbo; valgrind does, reporting `Invalid write ... 0 bytes after a block of size 65,569` from `jpeg_write_marker` called at `JpegEncode.c:330` before aborting on the corrupted heap metadata.

### Code path

The buffer. `JpegImagePlugin._save()` sizes the encoder buffer from the metadata it is about to emit, allowing one spare byte after the extra block and nothing for the comment:

```python # src/PIL/JpegImagePlugin.py:859-862 else: # The EXIF info needs to be written as one block, + APP1, + one spare byte. # Ensure that our buffer is big enough. Same with the icc_profile block. bufsize = max(len(exif) + 5, len(extra) + 1) ```

`ImageFile._save()` then takes `max(MAXBLOCK, bufsize, width*4)` (`src/PIL/ImageFile.py:662`, `MAXBLOCK = 65536`), and `_encode()` allocates exactly that: `buf = PyBytes_FromStringAndSize(NULL, bufsize)` (`src/encode.c:134`; the real-file path `_encode_to_file()` does `malloc(bufsize)` at `src/encode.c:190`). For the input above `len(extra) == 65516`, so the buffer is 65536 bytes.

The `optimize`/`progressive` branch just above (`JpegImagePlugin.py:846-858`) is not immune: its `bufsize` adds `w*h` (or `2*w*h`), but the image dimensions and the ICC length both come from the file, so an exact fit is still constructible there (e.g. with a 19×1 image).

The "+1 spare byte" does not account for what libjpeg itself has already put in the buffer: in state 1 `jpeg_start_compress(&cinfo, TRUE)` (`JpegEncode.c:279`) emits SOI + JFIF APP0, 20 bytes for an RGB source. State 3 then copies the extra block, clamped to the space remaining:

```c // src/libImaging/JpegEncode.c:302-337 case 3: if (context->extra) { unsigned int n = context->extra_size - context->extra_offset; if (n > context->destination.pu

Affected package ranges reported by GitHub: Pillow: >= 9.4.0, < 13.0.0

Scores and how they were measured

CVSS base severity

7.7

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/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

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 42.8%

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-g7cr-3p24-7wf7 (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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, 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-g7cr-3p24-7wf7, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-96778 (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-2026-96778, 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: Heap buffer overflow writing JPEG comment after ICC profile fills buffer (CVE-2026-96778). https://kevwire.com/record/CVE-2026-96778

MLA

"Pillow: Heap buffer overflow writing JPEG comment after ICC profile fills buffer (CVE-2026-96778)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-96778.

Chicago

KEVWire. "Pillow: Heap buffer overflow writing JPEG comment after ICC profile fills buffer (CVE-2026-96778)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-96778.

Evidence summary (plain text)

Pillow: Heap buffer overflow writing JPEG comment after ICC profile fills buffer (Oct 22, 2026).
```
============================================================================
Heap buffer overflow writing JPEG comment after ICC profile fills buffer
Location: src/libImaging/JpegEncode.c:330 in ImagingJpegEncode()
Commit: a707c6b21c313880d0771e54965d142dd42358b6
============================================================================
```

A heap buffer overflow in Pillow's JPEG encoder lets anyone who can supply an image write up to 64 KB of bytes they choose, followed by the rest of the compressed image, past the end of a 64 KB heap buffer. The target is any application that re-saves the image as JPEG while keeping its colour profile. The reliable result is that the Python process is killed outright rather than raising an exception. Because the overwritten memory sits directly in front of function pointers that the encoder calls next, this could allow code execution, though the attached reproducer demonstrates only the crash.
CVSS 7.7 (version 4.0; evidence as of Oct 22, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-96778).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-96778&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-g7cr-3p24-7wf7: https://github.com/advisories/GHSA-g7cr-3p24-7wf7
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%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-2026-96778: https://nvd.nist.gov/vuln/detail/CVE-2026-96778
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=8000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-96778&date=2026-10-26
Record ID: CVE-2026-96778.
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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