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CVE-2026-34588 high CVSS 7.8

Out-of-Bounds Read in openexr (CVE-2026-34588)

Summary

Vulnerability in openexr (CVE-2026-34588). Successful exploitation can lead to full system takeover. Exploitable via wcount. Mitigation: upgrade to 3.4.9 or later.

Original description

The description as published by the source.

Summary

internal_exr_undo_piz() advances the working wavelet pointer with signed 32-bit arithmetic:

wavbuf += nx * ny * wcount;

Because nx, ny, and wcount are int, a crafted EXR file can make this product overflow and wrap. The next channel then decodes from an incorrect address. The wavelet decode path operates in place, so this yields both out-of-bounds reads and out-of-bounds writes.

Tested on commit 7820b7e1b93405ba1d551c43a945018226b75bc5

Technical Details

The vulnerable decode path is:

  1. internal_exr_undo_piz() sets wavbuf = decode->scratch_buffer_1.
  2. For each channel, it calls wav_2D_decode (wavbuf + j, ...).
  3. It then advances wavbuf with wavbuf += nx * ny * wcount.

The overflow happens in step 3. Once wavbuf is wrapped, the next channel's wavelet decode runs on the wrong address.

In the 14-bit wavelet path, wdec14_4() first reads:

  • *px
  • *p10
  • *p01
  • *p11

and then writes back to the same locations:

  • *px = ...
  • *p01 = ...
  • *p10 = ...
  • *p11 = ...

As a result, the bug is not just a crash-only invalid read. It is an out-of-bounds read/write condition.

Reproduction

piz_scanline_redzone.zip

Build exrcheck with ASAN and run:

❯ ./build-asan/bin/exrcheck /tmp/piz_scanline_redzone.exr
 file /tmp/piz_scanline_redzone.exr /home/pop/sec/openexr/src/lib/OpenEXRCore/internal_piz.c:373:19: runtime error: signed int…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-34588 has been found in openexr.
Attackers can target a specific entry point like wcount over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: upgrade openexr to 3.4.9 or later.
If unsure, ask your IT team or search "openexr CVE-2026-34588" on the vendor's site.

CVE-2026-34588 (openexr) — CWE-125 / CVSS v3 7.8
Attack vector: local / no user interaction
Attack surface: wcount / int / wavbuf / exrcheck
Patched: 3.4.9 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Out-of-bounds read (CWE-125) exists in openexr. Attackers reach the vulnerable code path via wcount.

📍 Affected scope

Check the vendor advisory for the affected versions of openexr. Attack surface: wcount / int / wavbuf / exrcheck.

🔥 Severity

Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 3.4.9.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'openexr' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'openexr' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で openexr を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade openexr to 3.4.9

    ステージング環境で 3.4.9 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

PyPI openexr
[{"type":"ECOSYSTEM","events":[{"introduced":"3.4.0"},{"fixed":"3.4.9"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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