SDL_image is a library to load images of various formats as SDL surfaces. In do_layer_surface() in src/IMG_xcf.c, pixel index values from decoded XCF tile data are used directly as colormap indices without validating them against the colormap size (cm_num). A crafted .xcf file with a small colormap and out-of-range pixel indices causes heap out-of-bounds reads of up to 762 bytes past the colormap allocation. Both IMAGE_INDEXED code paths are affected (bpp=1 and bpp=2). The leaked heap bytes are written into the output surface pixel data, making them potentially observable in the rendered image. This vulnerability is fixed with commit 996bf12888925932daace576e09c3053410896f8.
Weakness
The product reads data past the end, or before the beginning, of the intended buffer.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Sdl_image | Libsdl | * | 2026-04-02 (excluding) |
| Libsdl2-image | Ubuntu | esm-apps/xenial | * |
| Libsdl2-image | Ubuntu | questing | * |
| Libsdl3-image | Ubuntu | questing | * |
| Sdl-image1.2 | Ubuntu | esm-apps/xenial | * |
| Sdl-image1.2 | Ubuntu | questing | * |
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.