--- id: "CVE-2026-112392" kind: "vulnerability" aliases: ["CVE-2026-112392", "GHSA-27h8-gf7j-v5hc"] title: "Pillow: NULL dereference in ImagingExpand via rank filters on zero-size images" severity: "high" cvss: 8.2 epss: 0.0029100000392645597 exploited: false status: "open" category: "package" products: [{"name": "Pillow", "fixed": ["13.0.0"], "affected": "<= 12.3.0", "ecosystem": "pypi"}] ecosystems: ["pypi"] tags: ["cwe-476", "image-processing", "package", "pillow", "python", "web-apps"] not_affected_if: ["no-rank-filters-used", "no-user-supplied-crop-or-tiff", "pillow-version-13.0.0-or-later"] published_at: "2026-10-19T22:17:06+00:00" first_seen_at: "2026-10-23T19:11:32+00:00" updated_at: "2026-10-23T21:57:19+00:00" sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-27h8-gf7j-v5hc", "first_seen_at": "2026-10-23T19:11:32+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112392", "first_seen_at": "2026-10-23T21:57:19+00:00"}] --- # Pillow: NULL dereference in ImagingExpand via rank filters on zero-size images Pillow's median, min, max and rank filters crash the whole Python process with SIGSEGV when applied to an image with zero width or height. An attacker who controls crop coordinates or an uploaded multi-page TIFF can kill the worker process, a denial of service with no memory disclosure. _Summary, check and fix written by a model from the sources; labelled as such._ ## Affected - pypi:Pillow affected <= 12.3.0 fixed 13.0.0 ## How to check pip show pillow (affected if version <= 12.3.0) If an app calls ImageFilter.MedianFilter/MinFilter/MaxFilter/RankFilter on crops or uploaded TIFF pages, it is reachable ## Fix Upgrade Pillow to 13.0.0 or later (pip install -U 'pillow>=13.0.0') Until upgraded, validate crop boxes so left != right and upper != lower before rank filtering ## Timeline - 2026-10-23T19:11:32+00:00 ghsa https://github.com/advisories/GHSA-27h8-gf7j-v5hc - 2026-10-23T21:57:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112392 ## From the sources ``` ============================================================================ NULL dereference in ImagingExpand via rank filters on zero-size images Location: src/libImaging/Filter.c:79 in ImagingExpand() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ``` Applying Pillow's median, minimum, maximum or rank filter to an image with zero width or zero height crashes the whole Python process instead of raising an error. Empty images like this are easy to produce with ordinary calls, for example a crop box whose left and right edges (or top and bottom edges) are equal, or the second page of a crafted multi-page image file. An attacker who can supply crop coordinates or an uploaded file to an application that runs one of these filters can kill its worker process. The effect is a crash only, with no memory disclosure or corruption. The fault is in `ImagingExpand()` in `src/libImaging/Filter.c`. This is the edge-padding step that `RankFilter.filter()` always runs through the core `expand()` method, so `MedianFilter`, `MinFilter` and `MaxFilter` go through it too. It fills the margin by copying the input's edge pixels, reading `imIn->image[y][0]` and rows `0` / `ysize-1`, and never checks that the input has any pixels. For an empty image, `ImagingAllocateArray` leaves the line pointers NULL, so the first read dereferences NULL and the process dies with SIGSEGV, in every mode. Zero-size images reach this point through public API alone: - `Image.crop()`, `ImageOps.crop()` and `Image.new()`; - a multi-page TIFF opened by path whose second IFD declares `ImageLength = 0`, on which `seek(1)` and `load()` succeed. Every other `ImageFilter` returns an empty image for the same inputs. The zero-height case has crashed since the original PIL import, and the zero-width case since Pillow 4.3.0. This is separate from the `margin == 0` fix in #9755: the path is the same, but here the degenerate value is the image size rather than the kernel size. It has the same shape as the zero-dimension `ImagingOffset` crash fixed under GHSA-f87v-9578-p47w. The attached reproducer shows a one-pixel-wide control crop filtering normally, while four empty crops passed through the rank filters are each killed by SIGSEGV. A patch that returns early in `ImagingExpand` for empty input is included. ## Details `ImagingExpand()` (`src/libImaging/Filter.c`), the edge-padding helper that `ImageFilter.RankFilter` runs before the actual rank filter, reads the first pixel of each input line without checking that the input has any pixels. For an image with width 0 or height 0 the line pointers are NULL, so `Image.filter()` with `MedianFilter`, `MinFilter`, `MaxFilter` or `RankFilter` kills the interpreter with SIGSEGV instead of returning or raising: ```python from PIL import Image, ImageFilter im = Image.new("L", (10, 10)).crop((3, 0, 3, 10)) # size (0, 10); crop() accepts left == right im.filter(ImageFilter.MedianFilter(3)) # SIGSEGV ``` Under gdb on the stock build the fault is at `ImagingExpand (imIn=…, margin=1) at src/libImaging/Filter.c:105` (the `EXPAND(UINT8, image8)` expansion), called from `_expand_image` at `src/_imaging.c:1151`, with `imIn->xsize = 0` and `imIn->image[0] = 0x0`. The same happens for every mode the rank filters accept (`L`, `RGB`, `RGBA`, `I`, `F`), and the core `expand(m)` method with `m >= 1` crashes the same way in any mode, including `P`. The same input through `BoxBlur`, `GaussianBlur`, `Kernel`, `ModeFilter` and `UnsharpMask` returns a `(0, 10)` image; a `(1, 10)` crop through `MedianFilter` also returns normally. The unchecked edge reads date from the PIL import (`9a640e315`, 2010, so every Pillow release): the zero-height case has crashed since then, and the zero-width case since `fd907fbdc` ("Fix 0-width and 0-height images other way", Pillow 4.3.0), which stopped backing zero-width images with a dummy block and left their row pointers NULL. It is adjacent to the `margin == 0` divide-by-zero fix in #9755 — same `expand()` → `ImagingExpand()` path, but the unhandled degenerate value here is the image size rather than the kernel size. The path: ```python # src/PIL/ImageFilter.py:111-116 RankFilter.filter (MedianFilter/MinFilter/MaxFilter subclass it) image = image.expand(self.size // 2) return image.rankfilter(self.size, self.rank) ``` `expand(m)` with `m > 0` is `ImagingExpand(self->image, m)` (`src/_imaging.c:1142-1151`). It validates only `margin`, allocates an output of `(xsize+2*margin) × (ysize+2*margin)` — which is non-empty, so the allocation succeeds — and then fills the margin by replicating edge pixels of the input: ```c // src/libImaging/Filter.c:70-101 imOut = ImagingNewDirty(imIn->mode, imIn->xsize + 2 * margin, imIn->ysize + 2 * margin); … #define EXPAND_LINE(type, image, yin, yout) \ { \ for (x = 0; x < margin; x++) { \ imOut->image[yout][x] = imIn->image[yin][0]; \ // line 79 } \ … \ for (x = 0; x < margin; x++) { \ imOut->image[yout][margin + imIn->xsize + x] = \ imIn->image[yin][imIn->xsize - 1]; \ // [-1] when xsize == 0 } \ } #define EXPAND(type, image) \ { \ for (y = 0; y < margin; y++) { \ EXPAND_LINE(type, image, 0, y); \ // line 0 of a 0-line image } \ … for (y = 0; y < margin; y++) { \ EXPAND_LINE(type, image, imIn->ysize - 1, margin + imIn->ysize + y); \ // line -1 when ysize == 0 } \ } ``` Why the line pointers are NULL: `ImagingNewPrologueSubtype` callocs the `im->image` pointer array (`src/libImaging/Storage.c:216`, at least one entry), and `ImagingAllocateArray` returns before assigning any of them for an empty image: ```c // src/libImaging/Storage.c:423-426 /* 0-width or 0-height image. No need to do anything */ if (!im->linesize || !im->ysize) { return im; } ``` So with `xsize == 0` every `imIn->image[y]` is NULL and `imIn->image[yin][0]` faults; with `ysize == 0` the top-margin pass reads `imIn->image[0]` (the single calloc'd NULL slot) and faults the same way, and the bottom-margin pass would index `imIn->image[-1]`. `ImagingRankFilter` is never reached. Zero-size images are ordinary objects in Pillow and arrive at `filter()` through public API only: - `Image.crop(box)` rejects only inverted boxes (`src/PIL/Image.py:1385-1390`); `left == right` or `upper == lower` yields a 0×N / N×0 image. `ImageOps.crop(im, border)` with `border == width // 2`, and `Image.new(mode, (0, n))`, do the same. - From a file: `ImageFile.__init__` refuses a zero first-frame size (`src/PIL/ImageFile.py:167-173`), but `TiffImagePlugin._setup()` takes `ImageWidth`/`ImageLength` of every later IFD as-is on `seek()` (`src/PIL/TiffImagePlugin.py:1468-1481`). For an uncompressed page of an image opened by path, `ImageFile.load()` takes the mmap branch (`src/PIL/ImageFile.py:307, 325-347`) and `Image.core.map_buffer` builds an `8×0` core image without complaint (`src/map.c:127-141`), so `im.seek(1); im.load()` succeeds and a following `im.filter(ImageFilter.MedianFilter(3))` segfaults in `ImagingExpand` exactly as --- _Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_