# CVE-2026-66338: libsoup: A flaw was found in libsoup

CVE-2026-66338 is fixed in 10 products on 1 platform, first by ALAS2023-2026-3212, released November 7, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-66338
- Priority: High
- CVSS: n/a (important)
- EPSS: 0.0029
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 12, 2026

## Description

A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libsoup amzn 2023 | 2.72.0-6.amzn2023.0.16 | [ALAS2023-2026-3212](https://patchblox.com/security/data/fix/linux/alas2023-2026-3212.md) | Nov 7, 2026 |
| Linux | libsoup-debuginfo amzn 2023 | 2.72.0-6.amzn2023.0.16 | [ALAS2023-2026-3212](https://patchblox.com/security/data/fix/linux/alas2023-2026-3212.md) | Nov 7, 2026 |
| Linux | libsoup-debugsource amzn 2023 | 2.72.0-6.amzn2023.0.16 | [ALAS2023-2026-3212](https://patchblox.com/security/data/fix/linux/alas2023-2026-3212.md) | Nov 7, 2026 |
| Linux | libsoup-devel amzn 2023 | 2.72.0-6.amzn2023.0.16 | [ALAS2023-2026-3212](https://patchblox.com/security/data/fix/linux/alas2023-2026-3212.md) | Nov 7, 2026 |
| Linux | libsoup-doc amzn 2023 | 2.72.0-6.amzn2023.0.16 | [ALAS2023-2026-3212](https://patchblox.com/security/data/fix/linux/alas2023-2026-3212.md) | Nov 7, 2026 |
| Linux | libsoup3 amzn 2023 | 3.7.3-1.amzn2023 | [ALAS2023-2026-3240](https://patchblox.com/security/data/fix/linux/alas2023-2026-3240.md) | Nov 7, 2026 |
| Linux | libsoup3-debuginfo amzn 2023 | 3.7.3-1.amzn2023 | [ALAS2023-2026-3240](https://patchblox.com/security/data/fix/linux/alas2023-2026-3240.md) | Nov 7, 2026 |
| Linux | libsoup3-debugsource amzn 2023 | 3.7.3-1.amzn2023 | [ALAS2023-2026-3240](https://patchblox.com/security/data/fix/linux/alas2023-2026-3240.md) | Nov 7, 2026 |
| Linux | libsoup3-devel amzn 2023 | 3.7.3-1.amzn2023 | [ALAS2023-2026-3240](https://patchblox.com/security/data/fix/linux/alas2023-2026-3240.md) | Nov 7, 2026 |
| Linux | libsoup3-doc amzn 2023 | 3.7.3-1.amzn2023 | [ALAS2023-2026-3240](https://patchblox.com/security/data/fix/linux/alas2023-2026-3240.md) | Nov 7, 2026 |

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Data as of 2026-11-11T13:47:35Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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