CVE-2026-51538: EIPStackGroup OpENer 2.3.0 (commit 76b95cf) suffers from an Incorrect Access Control vulnerability in its hand

This week

CRITICAL 9.1REMOTEDOWNGRADE

CVE-2026-51538 is a critical-severity flaw (CVSS 9.1) affecting opener. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

EIPStackGroup OpENer 2.3.0 (commit 76b95cf) suffers from an Incorrect Access Control vulnerability in its handling of encapsulation sessions. When the server processes critical encapsulation commands, it verifies whether the provided session_handle exists in the global session list, but it fails to verify whether that handle belongs to the specific TCP connection issuing the request. Because there is no strong binding between a session handle and

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 56%)
CISA exploited list	No
Weakness	CWE-284
Published	2026-07-13
Last modified	2026-08-11

Publisher (CNA): MITRE · Vendor: opener project

Last updated 2026-08-11 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-13 22:16 UTCPublished CVE record published
2026-08-11 16:38 UTCUpdated Record last modified

opener project opener DOWNGRADE

Affected: 2.3.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.3.0

1. Check installed version

apt-cache policy opener || rpm -q opener || opener --version

2. No fixed release: DOWNGRADE to a release before 2.3.0 (Debian / Ubuntu)

apt-cache madison opener sudo apt install opener=<VERSION_BEFORE_2.3.0> sudo apt-mark hold opener

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list opener sudo dnf downgrade opener-<VERSION_BEFORE_2.3.0> sudo dnf versionlock add opener

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-51538?

opener: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-51538 being exploited?

CVE-2026-51538 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-51538 affect?

CVE-2026-51538 affects opener. Severity is critical (CVSS 9.1). EIPStackGroup OpENer 2.3.0 (commit 76b95cf) suffers from an Incorrect Access Control vulnerability in its handling of encapsulation sessions. When the server processes critical encapsulation commands, it verifies whether the provided sessio

How urgent is CVE-2026-51538?

Priority 53/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-51536 CRITICAL 9.1 DOWNGRADE In OpENer 2.3.0 (commit 76b95cf) when parsing incoming CIP (Common Industrial Protocol) network packets, the l
CVE-2026-51537 CRITICAL 9.1 DOWNGRADE EIPStackGroup OpENer 2.3.0 (commit 76b95cf) has an out-of-bounds read issue in Connection Manager handling of
CVE-2026-51540 CRITICAL 9.8 DOWNGRADE OpENer 2.3.0 (master branch up to commit 76b95cf) is vulnerable to a severe memory corruption issue caused by
CVE-2026-51541 CRITICAL 9.1 DOWNGRADE OpENer 2.3.0 (commit 76b95cf) has an out-of-bounds read issue in CIP message parsing when handling malformed e

References

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