CVE-2026-55373 OpenEXR: OpenEXRUtil SampleCountChannel endEdit() can loop forever on UINT_MAX sample counts
An attacker can cause an infinite loop and denial of service in OpenEXR by providing a specific sample count value that triggers an integer overflow in size calculation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55373?
CVE-2026-55373 is a medium-severity denial of service vulnerability in AcademySoftwareFoundation openexr, published on 25 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
OpenEXR is the reference implementation and specification for the EXR image format, widely used in the motion picture industry. Versions prior to 3.2.10, 3.3.12, and 3.4.13 contain an infinite-loop vulnerability in SampleCountChannel. The helper roundListSizeUp() rounds a sample-list size up to the next power of two using repeated unsigned left shifts, which terminates for normal values but fails for UINT_MAX: the sequence reaches 0x80000000, and the next left shift wraps the 32-bit value to 0. Because 0 remains less than UINT_MAX, the loop never progresses and never exits. The bug is reachable through public OpenEXRUtil APIs, either by editing the sample-count buffer through SampleCountChannel::Edit (whose destructor calls endEdit()) or by calling SampleCountChannel::set(x, y, UINT_MAX) on a valid pixel. This issue has been fixed in versions 3.2.10, 3.3.12, and 3.4.13.
Which versions are affected by CVE-2026-55373?
How do I fix CVE-2026-55373?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55373 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55373 exists.
Sources
Also known as AZL-97623, BELL-CVE-2026-55373, DEBIAN-CVE-2026-55373, ECHO-3c1f-3605-c2d9, GHSA-mff9-68x3-h8rh, MINI-rhff-q6mw-xchj and 1 more.