A specially-crafted file can cause libjxl's decoder to read pixel data from uninitialized (but allocated) memory.
This can be done by causing the decoder to reference an outside-image-bound area in a subsequent patches. An incorrect optimization causes the decoder to omit populating those areas.
Exploitability
AV:NAC:HAT:NPR:NUI:PVulnerable System
VC:LVI:LVA:NSubsequent System
SC:NSI:NSA:N2.3/CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:NOther