Which versions of Amazon.IonDotnet are affected by CVE-2025-11573?

Amazon.IonDotnet, a NuGet package used by .NET applications to parse Ion data, contains a denial-of-service vulnerability (CVE-2025-11573) that can cause application hangs and CPU exhaustion when…. A patch is available.

How to fix or mitigate CVE-2025-11573?

Within 24 hours, inventory all .NET applications using Amazon.IonDotnet versions prior to 1.3.2 and determine whether they parse untrusted Ion text; if so, immediately implement input validation to reject malformed Ion text encodings, especially for lobs and strings, and enforce strict timeouts and CPU limits on parsing threads. Within 7 days, for systems that cannot be immediately modified, consider disabling text-based Ion parsing and using only binary Ion if feasible, or isolate parsing in a separate process with resource constraints; monitor for CPU spikes and anomalous hangs. Within 30 days, migrate to a supported alternative Ion parsing library, as Amazon.IonDotnet is deprecated and will receive no further updates; if version 1.3.2 is available from a trusted source and verified to resolve the issue, test and deploy it, but note that no official vendor patch is available.

Amazon.IonDotnet CVE-2025-11573

Q: What is the CVSS score of CVE-2025-11573?

CVE-2025-11573 has a CVSS 4.0 base score of 8.7 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:X. EPSS exploitation probability: 0.4%.

HIGH

Improper Validation of Syntactic Correctness of Input (CWE-1286)

2025-10-09 ff89ba41-3aa1-4d27-914a-91399e9639e5

Denial Of Service

8.7

CVSS 4.0 · Vendor: ff89ba41-3aa1-4d27-914a-91399e9639e5

Severity by source

Vendor (ff89ba41-3aa1-4d27-914a-91399e9639e5) PRIMARY

8.7 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:X

vuln.today AI

7.5 HIGH

Untrusted Ion text is parsed remotely without auth or interaction (AV:N/AC:L/PR:N/UI:N); infinite loop yields availability-only impact (A:H, C:N/I:N), scope unchanged.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (ff89ba41-3aa1-4d27-914a-91399e9639e5).

CVSS VectorVendor: ff89ba41-3aa1-4d27-914a-91399e9639e5

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Analysis Generated

Oct 08, 2026 - 14:00 vuln.today

CVE Published

Oct 09, 2025 - 18:15 cve.org

HIGH 8.7

DescriptionCVE.org

An infinite loop issue in Amazon.IonDotnet library versions <v1.3.2 may allow a threat actor to cause a denial of service through a specially crafted text input.

To mitigate this issue, users should upgrade to version v1.3.2. As of August 20, 2025, this library has been deprecated and will not receive further updates.

AnalysisAI

A parser defect in the Amazon.IonDotnet NuGet package before version 1.3.2 lets remote, unauthenticated attackers hang a .NET application by feeding it specially crafted Ion text input, causing CPU exhaustion and denial of service on the parsing thread. The issue is triggered specifically by malformed text encodings of Ion lobs and strings (per upstream fix PR #160), not by binary Ion, so exposure depends entirely on whether untrusted Ion text reaches the library - systems that only parse Ion from trusted sources are not realistically exposed. The library was deprecated on August 20, 2025 and will receive no further updates; there is no confirmed active exploitation and no public exploit code identified at time of analysis, and EPSS is low at 0.43% (36th percentile), consistent with a moderate-severity availability issue rather than an emergency.

Technical ContextAI

Amazon Ion is a richly typed, self-describing data serialization format with both human-readable text and compact binary encodings, and Amazon.IonDotnet is AWS's .NET implementation of readers and writers for it. The defect is classified as CWE-1286 (Improper Validation of Syntactic Correctness of Input): when the text parser encountered an invalid input condition while reading lobs (binary large objects expressed in the text encoding) or strings, the error state was handled improperly and the parser looped indefinitely instead of failing fast, so the calling thread spins and consumes CPU rather than returning a parse error. Only the text encoding is affected; the binary Ion path is not implicated by the fix. The upstream patch (PR #160, commit edaff75fe5abbb71e647bed812c608c0c5e2fbab) corrects the loop handling in text parsing of lobs and strings and shipped in the v1.3.2 release. Because this is a library rather than a network service, the attack surface is any downstream application, service, or fork that deserializes attacker-influenced Ion text using an affected version; the CVSS 4.0 vector provided by the vendor is AV:N/AC:L/AT:N/PR:N/UI:N with only availability (VA:H) impacted, and our independent assessment concurs under CVSS 3.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), with no confidentiality or integrity loss.

Affected ProductsAI

Amazon.IonDotnet for .NET, distributed as the NuGet package nuget/Amazon.IonDotnet, is vulnerable in all versions below 1.3.2 (CPE-style identifier: cpe:2.3:a:amazon:iondotnet:*:*:*:*:*:nuget:*:* versions < 1.3.2; GHSA advisory GHSA-q5r6-9qwq-g2wj). Any application, service, or library that embeds an affected version - including forked or derivative code paths - is exposed wherever untrusted Ion text is parsed. The vendor advisory notes the package was deprecated as of August 20, 2025, so no versions after 1.3.2 should be expected; users should verify the resolved dependency version in their build (for example via NuGet package listing or lock file) and treat transitive references to Amazon.IonDotnet as in scope. Vendor references: https://aws.amazon.com/security/security-bulletins/AWS-2025-022/, https://github.com/amazon-ion/ion-dotnet/releases/tag/v1.3.2, and https://github.com/amazon-ion/ion-dotnet/security/advisories/GHSA-q5r6-9qwq-g2wj.

RemediationAI

Vendor-released patch: Amazon.IonDotnet 1.3.2 (https://www.nuget.org/packages/Amazon.IonDotnet/1.3.2), which fixes the infinite-loop handling in text parsing of lobs and strings via https://github.com/amazon-ion/ion-dotnet/pull/160 and commit edaff75fe5abbb71e647bed812c608c0c5e2fbab; upgrade any direct or transitive reference below 1.3.2 and confirm the resolved version in your lock file, and backport the commit into any fork or derivative code since the project is deprecated as of August 20, 2025 and will not receive further updates. Where upgrading is not immediately possible, the vendor workaround is to accept Ion data only from trusted sources that were written by a supported Ion library - effective, but it means the component cannot safely process third-party or user-supplied Ion text at all. Additional compensating controls with trade-offs: enforce strict input size limits and per-request parse timeouts or cancellation tokens so a hung parse is aborted rather than consuming a thread indefinitely (reduces but does not eliminate CPU blowup, and adds latency/error handling complexity), and isolate Ion parsing in a separate worker process or sandbox with CPU and wall-clock quotas that can be killed on timeout (adds operational overhead and deployment complexity). Binary Ion input is not affected by this specific flaw, so restricting ingestion to the binary encoding is a narrower mitigation where the data format is under your control. Advisory and coordination details: AWS security bulletin AWS-2025-022 and GHSA-q5r6-9qwq-g2wj.