OpenEXR has heap-buffer-overflow via signed integer underflow in ImfContextInit.cpp

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-26981: 0.60% estimated exploitation activity in the next 30 days; percentile 48.58 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A heap-buffer-overflow (OOB read) occurs in the istreamnonparallelread function in ImfContextInit.cpp when parsing a malformed EXR file through a memory-mapped IStream. A signed integer subtraction produces a negative value that is implicitly converted to sizet, resulting in a massive length being passed to memcpy. Affected Version - OpenEXR main branch (commit at time of testing) - src/lib/OpenEXR/ImfContextInit.cpp, lines 121–136 Root Cause ImfContextInit.cpp:121-126: sz is of type sizet (unsigned), but streamsz - nend yields a negative int64t value. This negative value is implicitly converted to sizet, wrapping around to a value close to 2^64, which is then passed to memcpy causing a heap-buffer-overflow. Suggested fix: sz = streamsz - nend → sz = streamsz - nread Reproduce Build OpenEXR as static libraries with ASAN enabled, then compile the PoC below. PoC Code: PoC Input: https://drive.google.com/file/d/1VhjdK11LA0LHdW1mJJIQEo64mc5tpOUV/view?usp=drivelink ASAN Log Impact…

Published by the source

6 Apr 2026, 17:51 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-q6vj-wxvf-5m8c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-q6vj-wxvf-5m8c

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# Patch Next advisory brief: CVE-2026-26981

Advisory: OpenEXR has heap-buffer-overflow via signed integer underflow in ImfContextInit.cpp
IDs: CVE-2026-26981, GHSA-q6vj-wxvf-5m8c
Record: https://patchnext.com/advisories/cve-2026-26981 (revision 2, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: openexr 3.4.5, 3.3.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI openexr: affected >= 3.3.0, < 3.3.7; >= 3.4.0, < 3.4.5; fixed in 3.3.7, 3.4.5

## Suggested inspection (read-only)
- `python -m pip show openexr`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on openexr.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-q6vj-wxvf-5m8c (OSV record GHSA-q6vj-wxvf-5m8c lists affected ranges: PyPI openexr >=3.3.0 =3.4.0 <3.4.5 (fixed))
- Verified: https://github.com/advisories/GHSA-q6vj-wxvf-5m8c (GitHub-reviewed advisory GHSA-q6vj-wxvf-5m8c lists affected ranges: PyPI openexr >=3.3.0 =3.4.0 <3.4.5)

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