Critical

Unvalidated peer value in Bouncy Castle MTI/A0 Diffie-Hellman agreement

IdentifiersCVE-2026-59650CWE-20· Improper Input Validation

CVE-2026-59650 is an improper input validation vulnerability in the MTI/A0 Diffie-Hellman agreement implementation in Bouncy Castle for Java before 1.85 and Bouncy Castle for Java LTS 2.73.0 through versions before 2.73.12. The implementation exponentiates a peer-supplied value without validating it, potentially undermining the security of the key agreement process. The vulnerability affects both release lines across all platforms.

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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.

Processing an unvalidated peer value during MTI/A0 Diffie-Hellman agreement may undermine the security of the key agreement process. Specific consequences, such as private-key recovery, disclosure of protected data, or modification of communications, are not established by the available vulnerability-specific information.

Mitigation

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

If immediate patching is not possible, avoid using the affected MTI/A0 Diffie-Hellman agreement functionality in untrusted or network-facing contexts until fixed versions are deployed. Where feasible, enforce strict validation of peer Diffie-Hellman public values at the application or protocol layer before passing them to the library, and prefer alternative key agreement mechanisms or code paths not affected by this issue. Mitigation details beyond upgrading are otherwise not currently available.

Remediation

Patch, then assume compromise.

Upgrade Bouncy Castle for Java to version 1.85 or later, or Bouncy Castle for Java LTS to version 2.73.12 or later. VMware Tanzu Data Flow on Kubernetes deployments should upgrade to version 2.1.5, which resolves this vulnerability.

PUBLIC EXPLOITS

Exploits

No valid public exploits. Mallory filtered out 1 candidate as fakes, detection scripts, or README-only repos.

VALID 0 / 1 TOTALView more in app

All candidate exploits were filtered out by Mallory's validation.

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

Bouncy CastleBc-Javaapplication

Bouncy CastleBouncy Castleapplication

Bouncy CastleBouncy Castle For Javaapplication

Bouncy CastleBouncy Castle For Java Ltsapplication

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

ACTIVITY FEED

Recent activity

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

11 SOURCESView more in app

ghsa syntheticNews

Aug 3, 2026

GHSA-ghgq-7g74-28wp

An MTI/A0 Diffie-Hellman agreement flaw in Bouncy Castle for Java caused by exponentiating an unvalidated peer value. It affects versions before 1.85 and Bouncy Castle for Java LTS versions before 2.73.12.

cvefeed high severityNews

Aug 3, 2026

CVE-2026-59650 - MTI/A0 DH agreement exponentiates unvalidated peer value

A vulnerability in Bouncy Castle for Java and Bouncy Castle for Java LTS where the MTI/A0 Diffie-Hellman agreement processes an unvalidated peer value, affecting versions before 1.85 and before 2.73.12 respectively.

What this page doesn’t show

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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 activity8