Summary
Pillow JPEG2000 tiled decode retains a growing scratch buffer and can be used for denial of service
src/libImaging/Jpeg2KDecode.c:853 accumulates total_component_width across every tile in a JPEG2000 image instead of recomputing it per tile. That accumulated value is then used in the tile_bytes calculation at src/libImaging/Jpeg2KDecode.c:868, which can make the decoder grow state->buffer via realloc at src/libImaging/Jpeg2KDecode.c:876 up to roughly one full image's decompressed size even when each tile is small. A crafted tiled JPEG2000 file can therefore force substantially higher transient memory usage and trigger out-of-memory failures during decoding. Based on current evidence, the supported impact is denial of service, not memory corruption.
Details
- Location:
src/libImaging/Jpeg2KDecode.c:853 - Root cause:
total_component_widthis initialized only once before the tile loop and keeps growing across tiles. It is then used to derivetile_bytes, so later tiles are treated as if they had the combined component width of all earlier tiles. - Dangerous operation:
tile_bytesis promoted intotile_info.data_size, thenstate->bufferis grown withreallocatsrc/libImaging/Jpeg2KDecode.c:876. - Reachability: any attacker-controlled JPEG2000 image with many tiles reaches this path during normal
Image.open(...).load()decoding.
PoC
The attached helper script and testcase were used:
exercise_j2k_tile_realloc.zip
Generate the testcase:
pythonexercise_j2k_tile_realloc.py make poc_3664_rgba_tile1832.jp2 \
--size 3664 --tile 1832
Expected geometry from the helper:
- image size:
3664 x 3664 - mode:
RGBA - tile size:
1832 x 1832(2x2tiles) image_bytes=53699584- uncapped RSS observed:
- vulnerable build:
maxrss_kb=180264 - fixed comparison build:
maxrss_kb=138404
- vulnerable build:
Load it with the current vulnerable build:
python exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2
Load it again under a 160 MB address-space cap:
python exercise_j2k_tile_realloc.py load poc_3664_rgba_tile1832.jp2 --limit-mb 160
Impact
Conservative impact: denial of service through memory exhaustion during JPEG2000 decoding.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-59204? CVE-2026-59204 is a high-severity allocation of resources without limits or throttling vulnerability in pillow (pip), affecting versions >= 8.2.0, < 12.3.0. It is fixed in 12.3.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- Which versions of pillow are affected by CVE-2026-59204? pillow (pip) versions >= 8.2.0, < 12.3.0 is affected.
- Is there a fix for CVE-2026-59204? Yes. CVE-2026-59204 is fixed in 12.3.0. Upgrade to this version or later.
- Is CVE-2026-59204 exploitable, and should I be worried? Whether CVE-2026-59204 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59204 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59204? Upgrade
pillowto 12.3.0 or later.