Pillow EUVD-2026-107566

Exploitation requires an application to re-save an attacker-supplied JPEG using Pillow (9.4.0 through 12.x) while preserving BOTH the image's ICC profile AND a forwarded COM comment. The triggering condition is highly specific: the ICC profile must be sized so it exactly fills the 65536-byte encoder buffer, leaving the COM marker to be written when libjpeg's free_in_buffer counter has been exhausted and then wraps. LIMITING FACTORS: the attack depends on this precise buffer-fill boundary (reflected as AT:P in the CVSS 4.0 vector) and on the host application actively re-encoding/round-tripping the image with metadata preserved (UI:P), making it application-behavior-dependent rather than exploitable against a passive library install; reliable code execution further depends on runtime and heap layout, so a process crash is the more consistently achievable impact.

This is a genuine memory-corruption flaw (CWE-787 out-of-bounds write) with a write primitive confirmed directly in the source diff: ImagingJpegEncode() in JpegEncode.c wrote a COM marker without first checking free_in_buffer against comment_size+5, and the fix adds exactly that bounds check. The CVSS 4.0 base score is 7.7 (High) with AV:N/AC:L/AT:P/PR:N/UI:P and full H/H/H vulnerable-system impact, reflecting a network-reachable, unauthenticated issue that nonetheless carries a real attack requirement (AT:P) and passive user/application interaction (UI:P). Several real-world mitigating signals cut against treating this as top-priority: no EPSS score was supplied in the input (exploitation probability unknown), the CVE is NOT in CISA KEV, and no public POC/exploit code is referenced - so exploitation status is 'no public exploit identified at time of analysis.' The precondition is narrow and precise: the ICC profile must exactly fill the 65536-byte encoder buffer so that libjpeg writes one byte past an exhausted counter that then wraps - a fragile, heap-layout-dependent condition. The description itself hedges RCE as 'may enable code execution in suitable runtime and heap layouts,' so reliable code execution is unconfirmed and a process crash (DoS) is the more probable practical outcome. Net: a real bug worth patching promptly given Pillow's enormous footprint, but currently a high-CVSS issue without evidence of weaponization or widespread exploitation.

An attacker uploads a crafted JPEG whose ICC profile is sized to exactly fill Pillow's 65536-byte JPEG encoder buffer and which also carries a forwarded COM comment, to a web service that uses Pillow to re-save uploaded images as JPEG while preserving metadata. When the server re-encodes the image, the COM marker write overruns the buffer and corrupts adjacent heap memory, crashing the worker and potentially enabling code execution depending on heap layout. No public exploit code is referenced in the provided intelligence.