CVE-2026-92454: The GUIX software JPEG decoder reads four kinds of marker segment without checking that each is long enough to hold what

The GUIX software JPEG decoder reads four kinds of marker segment without checking that each is long enough to hold what it reads. A truncated segment is therefore read past the end of the caller's image buffer. Separately, a zero chroma sampling factor makes the block decode loop non-terminating. Both reproduce in the default configuration, in which GX_SOFTWARE_DECODER_SUPPORT is enabled.