Vulnerability in openexr (CVE-2026-26981)
Summary
Vulnerability in openexr (CVE-2026-26981). Risk of unauthorized operations or information disclosure. Exploitable via istream_nonparallel_read. Mitigation: upgrade to 3.4.5 or later.
Original description
The description as published by the source.
Summary
A heap-buffer-overflow (OOB read) occurs in the istream_nonparallel_read 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 size_t, 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:
int64_t stream_sz = s->size (); // e.g., 21 (actual file size)
int64_t nend = nread + (int64_t)sz; // e.g., 17 + 4096 = 4113
if (stream_sz > 0 && nend > stream_sz)
{
sz = stream_sz - nend; // 21 - 4113 = -4092 (signed)
}
// ...
memcpy (buffer, data, sz); // sz is size_t → wraps to 0xFFFFFFFFFFFFF004
sz is of type size_t (unsigned), but stream_sz - nend yields a negative int64_t value. This negative value is implicitly converted to size_t, wrapping around to a value close to 2^64, which is then passed to memcpy causing a heap-buffer-overflow.
Suggested fix: sz = stream_sz - nend → sz = stream_sz - nread
Reproduce
Build OpenEXR as static libraries with ASAN enabled, then compile the PoC below.
PoC Code:
#include
#include
#include
#include
#include
#include
OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_ENTER
class MemMapIStream : public IStream
{
public:
MemMapIStr…
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
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-2026-26981 has been found in openexr.
Attackers can target a specific entry point like istream_nonparallel_read over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade openexr to 3.4.5 or later.
If unsure, ask your IT team or search "openexr CVE-2026-26981" on the vendor's site.
CVE-2026-26981 (openexr) — CWE-195
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: istream_nonparallel_read / ImfContextInit.cpp / IStream / size_t
Patched: 3.4.5 — 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.
A vulnerability (CWE-195) exists in openexr. Attackers reach the vulnerable code path via istream_nonparallel_read without authentication.
Check the vendor advisory for the affected versions of openexr. Attack surface: istream_nonparallel_read / ImfContextInit.cpp / IStream / size_t.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 3.4.5.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
-
1Identify 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。 -
2Apply patch patch
Upgrade openexr to 3.4.5ステージング環境で 3.4.5 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。
-
3Post-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
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com