CVE-2026-19643 Overview
CVE-2026-19643 is an out-of-bounds read vulnerability in the Base64 decoder of the Amazon aws-sdk-cpp library. Versions prior to 1.11.862 are affected on some platforms. A remote authenticated user can send crafted Base64-encoded input that causes an application processing the input to crash. The flaw is classified as CWE-125 (Out-of-bounds Read) and affects availability without impacting confidentiality or integrity. Amazon addressed the issue in aws-sdk-cpp release 1.11.862, published alongside AWS Security Bulletin 2026-080.
Critical Impact
A remote authenticated attacker can crash any application built on vulnerable aws-sdk-cpp versions by supplying malformed Base64 input, producing a denial-of-service condition.
Affected Products
- Amazon aws-sdk-cpp versions prior to 1.11.862
- Applications embedding vulnerable versions of the AWS SDK for C++ on affected platforms
- Downstream services and tools that process untrusted Base64-encoded input using aws-sdk-cpp
Discovery Timeline
- 2026-08-12 - CVE CVE-2026-19643 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-19643
Vulnerability Analysis
The vulnerability resides in the Base64 decoder shipped with the AWS SDK for C++. The decoder reads beyond the bounds of its input buffer when processing specifically crafted Base64-encoded data. On affected platforms, this out-of-bounds read triggers a memory access fault that terminates the host process.
Because the AWS SDK for C++ is widely embedded in server-side applications, agents, and command-line tools, the flaw exposes a broad range of downstream software. Any code path that decodes Base64 input controlled by an authenticated remote user constitutes a viable entry point. The impact is limited to availability: memory contents are not returned to the attacker, and no integrity primitive is provided.
Exploitation requires authenticated access and specific platform conditions, which increases attack complexity. Nevertheless, in multi-tenant services or shared APIs, an authenticated user can repeatedly crash a target process to sustain a denial-of-service condition.
Root Cause
The root cause is missing or incorrect bounds validation in the Base64 decoding routine. The decoder assumes input conforms to expected Base64 length and padding invariants. Crafted input that violates those invariants causes the routine to read past the allocated buffer, producing undefined behavior that, on affected platforms, results in a segmentation fault. See GitHub Security Advisory GHSA-mxm9-xpf9-x66x for the maintainer analysis.
Attack Vector
The attack vector is network-based and requires low-privileged authenticated access. An attacker submits crafted Base64 data through any application-exposed field that ultimately reaches the SDK's decoder — for example, request payloads, headers, or configuration data forwarded to AWS APIs. The decoder dereferences memory outside the input buffer, and the process terminates. No user interaction is required.
Refer to the maintainer advisory and release notes for technical specifics; no verified exploit code has been published.
Detection Methods for CVE-2026-19643
Indicators of Compromise
- Unexpected SIGSEGV crashes or abnormal process terminations in services linking aws-sdk-cpp versions prior to 1.11.862
- Repeated crash-restart cycles correlated with inbound requests containing malformed Base64 payloads
- Core dumps referencing Base64 decoding functions inside the aws-sdk-cpp call stack
Detection Strategies
- Inventory build dependencies to identify binaries linking aws-sdk-cpp below 1.11.862, including static and vendored copies
- Inspect application logs for parser exceptions or crash signatures originating from Base64 decoding paths
- Correlate authenticated user activity with process restart events to identify potential abuse patterns
Monitoring Recommendations
- Enable crash reporting and core-dump collection on services that process user-supplied Base64 content
- Forward process lifecycle telemetry and application logs into a centralized analytics platform for pattern analysis
- Alert on sustained increases in decode failures or process restarts tied to a single authenticated principal
How to Mitigate CVE-2026-19643
Immediate Actions Required
- Upgrade aws-sdk-cpp to version 1.11.862 or later and rebuild all dependent applications
- Audit deployed binaries and container images for embedded vulnerable versions of the SDK
- Restrict or rate-limit authenticated endpoints that accept Base64-encoded input until patches are deployed
Patch Information
Amazon released the fix in aws-sdk-cpp1.11.862. Download details are available at the GitHub Release 1.11.862 page. Additional vendor guidance is published in AWS Security Bulletin 2026-080.
Workarounds
- Validate and constrain Base64 input length and character set at the application boundary before passing data to the SDK
- Isolate services processing untrusted Base64 input using process supervisors that automatically restart on crash
- Reduce exposure by requiring stronger authentication or per-tenant quotas on endpoints that invoke the decoder
# Example: upgrade aws-sdk-cpp via vcpkg and rebuild application
vcpkg update
vcpkg upgrade aws-sdk-cpp --no-dry-run
cmake --build build --target clean
cmake --build build --config Release
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
