Medium

Pre-auth heap out-of-bounds write in Open62541 PubSub JSON decoder

IdentifiersCVE-2026-1301CWE-787· Out-of-bounds Write

CVE-2026-1301 is an out-of-bounds write in o6 Automation GmbH’s Open62541 affecting builds where both PubSub and JSON are enabled. A crafted PubSub JSON message can trigger the JSON decoder to write past the end of a heap-allocated array prior to authentication, resulting in memory corruption and a reliable process crash (DoS). Affected versions are Open62541 >= 1.5-rc1 and < 1.5-rc2.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation causes a reliable denial of service via process crash and corrupts memory due to a heap out-of-bounds write occurring pre-authentication. Depending on surrounding code and mitigations, memory corruption may present additional exploitation potential beyond DoS, but this is not established in the provided content.

Mitigation

If you can’t patch tonight, do this now.

Reduce attack surface by disabling JSON and/or PubSub features where feasible. Restrict and segment access to any interfaces that accept PubSub JSON messages (e.g., limit to trusted networks/clients), and follow ICS hardening guidance such as minimizing network exposure, placing control networks behind firewalls, isolating from business networks, and using secure remote access (e.g., updated VPN) when required.

Remediation

Patch, then assume compromise.

Upgrade to a non-vulnerable Open62541 release (i.e., a fixed version at or after 1.5-rc2, per the affected range >= 1.5-rc1 and < 1.5-rc2).

PUBLIC EXPLOITS

Exploits

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

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VendorProductType

AnyAnyhardware

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ACTIVITY FEED

Recent activity

1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

1 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity