Metalama: Deserialization of Untrusted Data (CVE-2026-62848)
Published Last modified Sources: OSV, Hersteller, CVE.org
What is affected, what to do
Update metalama.framework to version 2026.1.19, Metalama.Framework to version 2026.0.25.
- Affected
- Metalama
gte 2023.0.101-rc, < 2025.1.18..*
- Metalama
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Metrics
7.3
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
7.3
CVSS v3
Severity High on the scale from 0 to 10.
Source: OSV, Hersteller, CVE.org
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 8.3
Show all metrics
- Severity
- High
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 67.06 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 7.3 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 7.3
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.2 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 8.3
- Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-502, CWE-913
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
Summary
Metalama uses a local named-pipe channel to communicate between its Visual Studio processes — the Visual Studio UI process (devenv), the out-of-process Roslyn code-analysis process, and the CodeLens process. This channel deserialized messages from the pipe without restricting which CLR types could be instantiated. A local process able to write to the pipe can send a crafted message that instantiates arbitrary .NET types — a deserialization primitive in the same class as BinaryFormatter (CWE-502), and a well-known gadget-chain code-execution vector.
The flaw is present, via two successive serializers, in every Metalama release from the first public version (2023.0) up to and including 2026.1.18, and is fixed in 2026.1.19.
The pipe name is predictable: Metalama_{role}_{processId}_{hash(PackageVersion)}, derived from the public package version and a locally-enumerable process id. This channel is used by the Visual Studio integration only (Windows named pipes); it is not used for command-line / MSBuild builds.
Mechanisms
JSON era — Metalama 2023.0 through 2026.0.x (Newtonsoft.Json). The pipe formatter enabled polymorphic type embedding:
formatter.JsonSerializer.TypeNameHandling = TypeNameHandling.All; // ServiceEndpoint.cs (early), later BaseEndpoint.cs
The accompanying SerializationBinder (added later for multi-version assembly support) only remapped assembly names; its BindToType resolved any type name from the wire (assembly.GetType(typeName)) with no type allow-list. TypeNameHandling.All is the canonical unsafe-deserialization setting and has publicly available gadget chains (e.g. ysoserial.net), so this era is at least as exploitable as the later one. (Introduced by commit 0554368737, first shipped in release/2023.0.101-rc.)
MessagePack era — Metalama 2026.1.0 through 2026.1.18. The 2026.1 line migrated the pipe serialization to MessagePack (PR #1299, commit 117b607805, 2026-01-29), using typeless MessagePack (TypelessObjectResolver), which likewise embeds CLR type names on the wire and instantiates arbitrary types on receipt — again with no allow-list.
Both mechanisms share the same channel, the same predictable pipe name, the same impact, and the same access preconditions.
Impact
Potential arbitrary code execution inside the Visual Studio process that hosts the affected component (the UI process, the code-analysis process, or the CodeLens process), with full loss of confidentiality, integrity and availability within that process.
Mitigating factor (limits practical severity to Medium): the pipe is created with the default Windows ACL (no explicit PipeSecurity), which permits only same-user processes to write. All of the Visual Studio processes involved run as the same logged-in developer, so exploitation requires the attacker to already be executing code as that same user. There is no privilege escalation and no crossing of a security boundary; the practical value is code execution inside the developer's Visual Studio session (lateral movement / persistence within an already same-user-compromised context). This is why the practical severity is Medium despite the CVSS base score.
Severity
CVSS v3.1: AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H = 7.3 (High) base score; practical severity Medium, because the attacker gains no privilege beyond what they already had (same user, same Visual Studio session).
CVSS v4.0 cross-check: CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N = 7.0 (High). The Subsequent-System metrics are None because no security boundary is crossed.
Affected products and remediation
All affected products are part of the Visual Studio integration.
| Product | Affected | Remediation |
|---|---|---|
NuGet Metalama.Framework | all < 2026.1.19 | upgrade to 2026.1.19 (no backports) |
VS extension PostSharpTechnologies.PostSharp ("Metalama + PostSharp", maintained) | 2024.1 - 2026.1.4 | update to 2026.1.5 (bundles Metalama 2026.1.19) |
VS extension PostSharpTechnologies.Metalama (retired) | all versions | uninstall / migrate to PostSharp >= 2026.1.5 |
VS extension PostSharpTechnologies.caravela (retired) | all versions | uninstall / migrate to PostSharp >= 2026.1.5 |
The PostSharp extension was a separate, Metalama-free product before the 2024.1 merge (Metalama.Vsx issue #33843), so earlier PostSharp versions are not affected. GitHub has no Visual Studio Marketplace ecosystem, so only the NuGet package appears in the structured "Affected products" list.
Fix
Fixed in Metalama 2026.1.19 (commit d97f52e1b5, PR #1651): the type-name deserialization is wrapped in RpcContractMessagePackOptions, which enforces a [RpcContract] type allow-list on the wire; pipe access is restricted to the current user. The fix reaches the maintained Visual Studio extension in version 2026.1.5. The retired Caravela and Metalama extensions will not be fixed.
Source: OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| metalama | Metalama |
|
|
| nuget | metalama.framework |
|
|
Weakness classes (CWE)
CWE-502Deserialization of Untrusted Data
Base
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
Entry at MITRE CWE-502CWE-913Improper Control of Dynamically-Managed Code Resources
Class
The product does not properly restrict reading from or writing to dynamically-managed code resources such as variables, objects, classes, attributes, functions, or executable instructions or statements.
Entry at MITRE CWE-913
References & sources
- github.commetalama/Metalama/commit/5b4ced29f2b25631cc2e44d05b0fd5fe838b6c…x_refsource_MISC, web
- github.commetalama/Metalama/commit/d97f52e1b53ffe4176b2b05c56ffdf1ccd2f53…x_refsource_MISC, web
- github.commetalama/Metalama/pull/1651x_refsource_MISC, web
- github.commetalama/Metalama/releases/tag/release/2025.1.18x_refsource_MISC, web
- github.commetalama/Metalama/releases/tag/release/2026.0.25x_refsource_MISC, web
- github.commetalama/Metalama/releases/tag/release/2026.1.19x_refsource_MISC, web
- github.commetalama/Metalama/security/advisories/GHSA-h26j-4vp7-x9w2x_refsource_CONFIRM, web
- NVD (NIST)vuln/detail/CVE-2026-62848advisory
- github.commetalama/Metalamapackage
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
ReceivedGitHub
CVSS V3.1: AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
Weakness type: CWE-913, CWE-502
Description added or changed
New references:- https://github.com/metalama/Metalama/commit/5b4ced29f2b25631cc2e44d05b0fd5fe838b6cbe
- https://github.com/metalama/Metalama/commit/d97f52e1b53ffe4176b2b05c56ffdf1ccd2f53a9
- https://github.com/metalama/Metalama/pull/1651
- https://github.com/metalama/Metalama/releases/tag/release/2025.1.18
and 3 more references
Show 12 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —Metalama is a Roslyn-based open-source patterns and architecture toolkit for C#. From 2023.0.101-rc until 2025.1.18, 2026.0.25 and 2026.1.19, the Windows Visual Studio integration deserializes local named-pipe messages without restricting which CLR types can be instantiated. The pipe connects `devenv`, the out-of-process Roslyn code-analysis process and the `CodeLens` process, and has the predictable name `Metalama_{role}_{processId}_{hash(PackageVersion)}`. Releases from the first public 2023.0 line through 2026.0.x use Newtonsoft.Json with `TypeNameHandling.All`; the later `SerializationBinder` only remaps assembly names, and `BindToType` resolves arbitrary wire-supplied types without an allow-list. Releases 2026.1.0 through 2026.1.18 use typeless MessagePack with `TypelessObjectResolver` and likewise instantiate arbitrary types. A same-user local process able to write to the pipe can send crafted messages that lead to arbitrary code execution with confidentiality, integrity and availability impacts inside the affected Visual Studio process. Default Windows pipe ACLs limit writers to the same logged-in user, so this does not escalate privileges or cross a security boundary; command-line and MSBuild-only builds do not use the channel. The maintained Metalama + PostSharp extension is affected from 2024.1 through 2026.1.4, while earlier Metalama-free PostSharp versions are unaffected. The retired Metalama and Caravela extensions remain affected and require removal or migration. The framework issue is fixed in versions 2025.1.18, 2026.0.25 and 2026.1.19; the maintained Metalama + PostSharp Visual Studio extension is fixed in version 2026.1.5. The retired Metalama and Caravela extensions require removal or migration.CVSS added —AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:HWeakness type (CWE) added —CWE-913Weakness type (CWE) added —CWE-502Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/62xxx/CVE-2026-62848.json">CVE-2026-62848</a>Reference added —https://github.com/metalama/Metalama/commit/5b4ced29f2b25631cc2e44d05b0fd5fe838b6cbeReference added —https://github.com/metalama/Metalama/commit/d97f52e1b53ffe4176b2b05c56ffdf1ccd2f53a9Reference added —https://github.com/metalama/Metalama/pull/1651Reference added —https://github.com/metalama/Metalama/releases/tag/release/2025.1.18Reference added —https://github.com/metalama/Metalama/releases/tag/release/2026.0.25Reference added —https://github.com/metalama/Metalama/releases/tag/release/2026.1.19Reference added —https://github.com/metalama/Metalama/security/advisories/GHSA-h26j-4vp7-x9w2Source identifier: security-advisories@github.com
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-62848"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-62848.svg?lang=en" alt="CVE-2026-62848 – NEOSEC Intel" height="20"></a>