High

.NET out-of-bounds read denial of service

IdentifiersCVE-2026-26127CWE-125· Out-of-bounds Read

CVE-2026-26127 is a publicly disclosed denial-of-service vulnerability in Microsoft .NET caused by an out-of-bounds read. The provided content indicates the issue affects .NET 9.0 and 10.0 on Windows, macOS, and Linux, and also affects Microsoft.Bcl.Memory versions 9.0 and 10.0. Supporting advisory content further states the flaw is triggered when decoding malformed Base64Url input in .NET and Microsoft.Bcl.Memory. A remote, unauthenticated attacker can send specially crafted network input to a vulnerable .NET application, causing the out-of-bounds read and crashing the application or service.

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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 allows an unauthenticated remote attacker to cause denial of service by crashing vulnerable .NET applications or services, disrupting availability. The available content describes the immediate impact as service interruption or application crash rather than code execution or privilege escalation. Multiple sources in the content note Microsoft assessed exploitation as unlikely and there was no evidence of active exploitation at the time of reporting.

Mitigation

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

If immediate patching is not possible, reduce exposure of vulnerable .NET services to untrusted network input, especially endpoints that process attacker-controlled Base64Url data. Monitor application, system, and network logs for unexpected crashes or malformed request patterns indicative of attempted denial-of-service exploitation. Prioritize internet-exposed services for patching. The provided content does not describe a complete vendor-supported workaround short of updating the runtime and/or affected Microsoft.Bcl.Memory package.

Remediation

Patch, then assume compromise.

Apply Microsoft's security updates. Based on the provided content, upgrade .NET 9.0 to 9.0.14, .NET 10.0 to 10.0.4, and update Microsoft.Bcl.Memory to patched versions 9.0.14 or 10.0.4 as applicable. Rebuild and redeploy applications after updating dependencies where Microsoft.Bcl.Memory is used. Ensure affected runtimes/SDKs and NuGet package dependencies are updated across supported Windows, macOS, and Linux deployments.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

Microsoft CorporationBcl Memoryapplication

Microsoft CorporationBcl.Memoryapplication

Microsoft CorporationNetapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

58 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

58 SOURCESView more in app

cyber security newsNews

Apr 16, 2026

31 High-Impact Vulnerabilities Exploited in March as Interlock Hits Cisco FMC Zero-Day

An actively exploited out-of-bounds read vulnerability affecting Microsoft .NET 9.0/10.0 and Microsoft.Blazor.Memory.

sentinelone blogNews

Mar 13, 2026

The Good, the Bad and the Ugly in Cybersecurity - Week 11

A .NET denial-of-service vulnerability disclosed in Microsoft's Patch Tuesday release.

bank info securityNews

Mar 12, 2026

Breach Roundup: Russian State Actors Target Signal, WhatsApp

A denial-of-service vulnerability in Microsoft .NET that could allow an attacker to disrupt services through an out-of-bounds read.

govinfosecurityNews

Mar 12, 2026

Breach Roundup: Russian State Actors Target Signal, WhatsApp

A denial-of-service vulnerability in Microsoft .NET that could allow an attacker to disrupt services through an out-of-bounds read.

+14 more in the timeline

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

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

Social activity33

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-26127

NVD

nvd.nist.gov/vuln/detail/CVE-2026-26127

MITRE CWE · CWE-125

Out-of-bounds Read

Vendor Advisory

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26127