CVE-2026-19642: AWS SDK C++ Buffer Overflow Vulnerability

CVE-2026-19642 Overview

CVE-2026-19642 is an out-of-bounds write vulnerability [CWE-787] in the Base64 decoder of the Amazon aws-sdk-cpp library before version 1.11.862. The flaw allows a remote authenticated user to trigger heap memory corruption or a process crash by supplying crafted Base64-encoded input to an application that relies on the SDK's decoder. Amazon Web Services (AWS) addressed the issue in aws-sdk-cpp release 1.11.862, and downstream applications must rebuild against the fixed version to remediate.

Critical Impact
Crafted Base64 input processed by vulnerable versions of aws-sdk-cpp can corrupt heap memory or crash the host application, degrading availability and creating conditions for further exploitation.

Affected Products

Amazon aws-sdk-cpp versions prior to 1.11.862
Applications statically or dynamically linking the vulnerable aws-sdk-cpp Base64 decoder
Downstream C++ services and tooling that process untrusted Base64-encoded input via the SDK

Discovery Timeline

2026-08-12 - CVE-2026-19642 published to NVD
2026-08-12 - Last updated in NVD database

Technical Details for CVE-2026-19642

Vulnerability Analysis

The defect resides in the Base64 decoding routine shipped with aws-sdk-cpp. When the decoder processes crafted Base64 input, it writes past the bounds of an allocated buffer, corrupting adjacent heap memory. The behavior is classified as an out-of-bounds write [CWE-787]. Exploitation requires the attacker to reach an application code path that decodes attacker-controlled Base64 content using the SDK. Successful triggering can crash the process or corrupt heap metadata and neighboring allocations, which can in turn destabilize the application or influence subsequent control-flow-sensitive operations.

Root Cause

The root cause is inadequate boundary validation in the Base64 decoder when computing or writing decoded output bytes. Malformed or specially sized inputs cause the decoder to produce more output bytes than the destination buffer accommodates, resulting in a heap-based out-of-bounds write. AWS resolved the flaw in aws-sdk-cpp1.11.862, per the GitHub Security Advisory GHSA-wxx3-prfc-69xx.

Attack Vector

The attack is network-reachable but requires authentication and constrained conditions. An attacker with valid credentials to a service that consumes Base64-encoded payloads through aws-sdk-cpp submits crafted input designed to trigger the decoder flaw. The immediate outcome is a crash or heap corruption within the target process. Refer to the AWS Security Bulletin 2026-080 for AWS's official guidance on impacted usage patterns.

No verified public exploit code is available. The vulnerability is described in prose per the vendor advisory; see the GitHub Release AWS SDK C++ 1.11.862 for the corresponding fix commits.

Detection Methods for CVE-2026-19642

Indicators of Compromise

Unexpected crashes, segmentation faults, or heap corruption aborts in C++ services linked against aws-sdk-cpp
Core dumps referencing Base64 decoding functions within the aws-sdk-cppAws::Utils::Base64 namespace
Anomalous authenticated requests carrying oversized or malformed Base64 payloads to internal APIs

Detection Strategies

Inventory build manifests, SBOMs, and container images to identify binaries linked to aws-sdk-cpp versions earlier than 1.11.862
Instrument affected services with AddressSanitizer (ASan) in non-production environments to surface out-of-bounds writes during Base64 decoding
Correlate application crash telemetry with authentication logs to identify low-privileged users submitting anomalous encoded payloads

Monitoring Recommendations

Forward application crash events and core dump metadata to a centralized logging pipeline for correlation with request-level telemetry
Alert on repeated process restarts or watchdog-triggered recoveries in services that decode Base64 input from users
Track outbound and inbound API payload sizes for services exposing Base64-accepting endpoints to detect abuse patterns

How to Mitigate CVE-2026-19642

Immediate Actions Required

Upgrade aws-sdk-cpp to version 1.11.862 or later and rebuild all dependent applications and container images
Audit internal services and third-party components that embed aws-sdk-cpp and prioritize those exposing authenticated Base64-accepting endpoints
Restrict access to endpoints that decode Base64 input to only trusted authenticated principals until patched builds are deployed

Patch Information

AWS released the fix in aws-sdk-cpp version 1.11.862. See the GitHub Release AWS SDK C++ 1.11.862 and the coordinated GitHub Security Advisory GHSA-wxx3-prfc-69xx. Application vendors must rebuild binaries against the patched SDK; runtime-only updates are insufficient for statically linked deployments.

Workarounds

Validate and constrain the length and character set of Base64 input at the application layer before passing it to the SDK decoder
Reject requests from unauthenticated or low-trust principals to code paths invoking Aws::Utils::Base64 decoding until patches are applied
Isolate services that process untrusted Base64 input in hardened process sandboxes to limit the blast radius of heap corruption

bash

# Configuration example: enforce patched aws-sdk-cpp version in vcpkg manifest
# vcpkg.json
{
  "name": "my-app",
  "version": "1.0.0",
  "dependencies": [
    {
      "name": "aws-sdk-cpp",
      "version>=": "1.11.862"
    }
  ]
}