CVE-2026-56758 is a heap over-read in MMS (Manufacturing Message Specification) stack AARQ/AP title parsing, triggered when the length value in the AP title field is zero or one. This causes the parser to read past buffer boundaries. The vulnerability requires an attacker to complete MMS connection establishment and specifically craft the AP title field — exploitation is not trivial and demands protocol knowledge that limits automated exploitation. The CVSS of 6.5 and low EPSS (0.00181) reflect this complexity, but these metrics miss the actual OT risk profile. In deployed ICS environments, MMS typically multiplexes with operator interfaces, engineering workstations, and historian connections over the same network paths. The more relevant question isn't 'will this be exploited' but 'what crashes when it triggers': a heap over-read in MMS processing can crash a PLC, and in continuous process environments that means an unplanned safety shutdown — a concrete operational consequence that may warrant patching priority beyond what CVSS suggests. The likely blast radius extends to every service sharing that network path. More importantly, this vulnerability almost certainly isn't isolated. The same length validation failure pattern exists in adjacent parsers within the same MMS stack — AARE response handling, ACSE services, other PDU types — and in vendor forks of MMS implementations across the ICS ecosystem. If you're maintaining an MMS stack, audit your AARQ response path and related PDU handlers for similar bounds check patterns. The patching question isn't whether to patch urgently; it's whether your network architecture treats MMS as trusted when it shares infrastructure with less-scrutinized services. Prioritize segmentation audits over pure CVSS-driven scheduling — that's where the actual exposure lies.
CVE-2026-56758
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedThe ACSE layer contains a flaw in the processing of AARQ PDUs during MMS connection establishment. When parsing certain fields within the calling AP title, an attacker controlled length value of zero or one may cause the parser to read past the end of a heap buffer.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisThe code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.
General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataThere is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.
Free. We build fixes in the order the community asks for them — and we’ll tell you the moment this one lands.
We develop and verify an original fix where the vendor hasn’t, from $2,850. Deployed to your staging first — never straight to production.
Scope it with usSee what else the community needs solved on the solutions-needed board.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-56758 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesCVE-2026-56758 is a heap over-read in MMS (Manufacturing Message Specification) stack AARQ/AP title parsing, triggered when the length value in the AP title field is zero or one. This causes the parser to read past buffer boundaries. The vulnerability requires an attacker to complete MMS connection establishment and specifically craft the AP title field — exploitation is not trivial and demands protocol knowledge that limits automated exploitation. The CVSS of 6.5 and low EPSS (0.00181) reflect this complexity, but these metrics miss the actual OT risk profile. In deployed ICS environments, MMS typically multiplexes with operator interfaces, engineering workstations, and historian connections over the same network paths. The more relevant question isn't 'will this be exploited' but 'what crashes when it triggers': a heap over-read in MMS processing can crash a PLC, and in continuous process environments that means an unplanned safety shutdown — a concrete operational consequence that may warrant patching priority beyond what CVSS suggests. The likely blast radius extends to every service sharing that network path. More importantly, this vulnerability almost certainly isn't isolated. The same length validation failure pattern exists in adjacent parsers within the same MMS stack — AARE response handling, ACSE services, other PDU types — and in vendor forks of MMS implementations across the ICS ecosystem. If you're maintaining an MMS stack, audit your AARQ response path and related PDU handlers for similar bounds check patterns. The patching question isn't whether to patch urgently; it's whether your network architecture treats MMS as trusted when it shares infrastructure with less-scrutinized services. Prioritize segmentation audits over pure CVSS-driven scheduling — that's where the actual exposure lies.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-56758 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data