CVE-2026-96641: Pillow: Reachable undefined behavior in native integer operations, potentially leading to denial of service or logic integrity compromise
Pillow is a Python imaging library. Prior to 13.0.0, PILfont text-width accumulation in src/imaging.c checks positive glyph advances against INTMAX but does not check negative advances against INTMIN. Repeating a signed 16-bit advance of -32768 can therefore execute a signed C integer overflow in xsize += dx, producing a large positive width from a negative mathematical result. Applications that use getlength(), getsize(), or derived layout, quota, serialization, or allocation calculations can experience logic-integrity errors or resource consumption, while the high-level mask path commonly retains a decompression-bomb check. This issue is fixed in version 13.0.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Pillowto a version that resolves this vulnerability.Fixed in 13.0.0
Event History
Frequently Asked Questions
Which applications are realistically exposed?
Applications using Pillow versions before 13.0.0 are exposed if they call PILfont text-measurement functionality such as getlength(), getsize(), or calculations derived from those results. Risk is greatest where those measurements feed layout, quotas, serialization, or allocation decisions.
What does exploitation require?
An attacker needs to cause repeated glyph advances of -32768 during text-width accumulation. The vector is network-reachable in affected applications that process attacker-influenced text or font-related inputs, and user interaction is required according to the supplied severity vector.
Is a denial of service the only possible impact?
No. The overflow can turn a negative mathematical width into a large positive value, which can cause logic-integrity errors as well as resource consumption or denial of service. The high-level mask path commonly retains a decompression-bomb check, but that does not eliminate risks in downstream layout, quota, serialization, or allocation handling.
What should teams do if they cannot immediately upgrade?
Avoid using affected text-width results in allocation, quota, serialization, or other security-sensitive decisions when processing untrusted inputs. Where possible, restrict or validate inputs that can trigger repeated negative glyph advances and impose resource limits around downstream processing.