CVE-2026-4269
Amazon Bedrock Agentcore Starter Toolkit ≤ 0.1.13
Raw vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XSummary
CVE-2026-4269 is a medium-severity Unverified Ownership (CWE-283) vulnerability in Amazon Bedrock Agentcore Starter Toolkit. Its CVSS base score is 5.8 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Web Cookies (T1606.001); ranked at the 16th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-24 (Access Control Decisions) and AC-25 (Reference Monitor) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-4269 stems from a missing S3 ownership verification in the Bedrock AgentCore Starter Toolkit prior to version v0.1.13. This flaw affects only users who build or have built the toolkit after September 24, 2025; those on version v0.1.13 or later, or who built earlier versions before that date, remain unaffected. The vulnerability enables code injection during the build process, resulting in arbitrary code execution within the AgentCore Runtime, and is associated with CWE-283 (Unverified Ownership) and CWE-340 (Generation of Predictable Numbers or Identifiers).
A remote attacker can exploit this over the network without privileges, though it demands high attack complexity and user interaction, per its CVSS v3.1 base score of 7.5 (AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H). By compromising the S3 verification step, the attacker injects malicious code into the build, achieving full code execution in the runtime environment with high impacts on confidentiality, integrity, and availability.
AWS advisories recommend upgrading to Bedrock AgentCore Starter Toolkit v0.1.13 as the sole remediation. Details are available in the AWS security bulletin at https://aws.amazon.com/security/security-bulletins/2026-008-AWS/ and the GitHub release notes at https://github.com/aws/bedrock-agentcore-starter-toolkit/releases/tag/v0.1.13.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12490
Vulnerability Data
A missing S3 ownership verification in the Bedrock AgentCore Starter Toolkit before version v0.1.13 may allow a remote actor to inject code during the build process, leading to code execution in the AgentCore Runtime. This issue only affects users of…
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the Bedrock AgentCore Starter Toolkit before version v0.1.13 who build or have built the Toolkit after September 24, 2025. Any users on a version >=v0.1.13, and any users on previous versions who built the toolkit before September 24, 2025 are not affected. To remediate this issue, customers should upgrade to version v0.1.13.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 10 hardening rules · 6 OS baselines
V11.3.4
Mitigating Controls (NIST 800-53 r5) AI
Access enforcement directly requires verifying ownership before granting access to resources.
Requiring access decisions to consider all relevant attributes includes ownership verification.
A reference monitor provides the tamperproof mechanism that can enforce ownership checks.
Developer testing and evaluation can discover predictable number generation through targeted analysis or fuzzing of identifier creation routines.
Cryptographic key establishment and management mandates proper entropy and randomness during generation, directly stopping predictable identifiers at the source.
Associating ownership as a security attribute enables subsequent verification of resource ownership.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Enforcing defined access permissions and authorizations directly prevents missing ownership verification for resources.
Secure SDLC practices directly require cryptographically strong RNG for identifiers and tokens, covering most of this weakness while the control addresses many additional development issues.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Cryptographic controls require use of approved, sufficiently random algorithms and key-generation methods, directly mitigating predictable number/identifier weaknesses.
Security testing in development can detect predictable identifiers through static/dynamic analysis and fuzzing, reducing residual risk.
Access control policies can require ownership verification before granting access to critical resources.
Identity management processes can include verification of resource ownership during provisioning and access decisions.
Access rights reviews can enforce checks that only legitimate owners retain privileges over critical assets.
Privileged access rights assignment should verify ownership to prevent unauthorized elevation on critical resources.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248524 OL 8 must implement NIST FIPS-validated cryptography for the following: To provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. prevents CWE-340
- V-248600 OL 8 must have the packages required to use the hardware random number generator entropy gatherer service. prevents CWE-340
RHEL 7 (1 rule)
- V-204497 The Red Hat Enterprise Linux operating system must implement NIST FIPS-validated cryptography for the following: to provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. prevents CWE-340
RHEL 8 (1 rule)
- V-244527 RHEL 8 must have the packages required to use the hardware random number generator entropy gatherer service. prevents CWE-340
Windows Server 2016 (1 rule)
- V-224831 Local volumes must use a format that supports NTFS attributes. prevents CWE-283
Windows Server 2019 (1 rule)
- V-205663 Windows Server 2019 local volumes must use a format that supports NTFS attributes. prevents CWE-283