withastro up to 4.0.18 RSS Feed Generation index.ts z.string source.title/enclosure.type injection

Summaryinfo

A vulnerability classified as critical has been found in withastro astro up to 4.0.18. This affects the function z.string of the file packages/astro-rss/src/index.ts of the component RSS Feed Generation. The manipulation of the argument source.title/enclosure.type leads to injection. This vulnerability is uniquely identified as CVE-2026-59728. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as critical, has been found in withastro astro up to 4.0.18. This issue affects the function z.string of the file packages/astro-rss/src/index.ts of the component RSS Feed Generation. The manipulation of the argument source.title/enclosure.type with an unknown input leads to a injection vulnerability. Using CWE to declare the problem leads to CWE-74. The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Astro is a web framework for content-driven websites. In versions 1.0.0 through 4.0.18, the source.title and enclosure.type item fields in packages/astro-rss/src/index.ts are interpolated directly into XML template strings without XML-character escaping before being parsed by fast-xml-parser. Both fields are validated only as z.string(), placing no restriction on XML special characters. An attacker who controls these values can inject arbitrary XML into the generated RSS feed: a value containing " can break out of an attribute (as with enclosure.type), and a value containing </source> can close an element early and inject additional nodes (as with source.title). This corrupts feed structure, injects false metadata (for example, a fake <link> pointing to a malicious URL), and can cause feed readers to misparse or display attacker-controlled content. In SSR mode (output: 'server'), the poisoned feed is served on every request to all subscribers. This issue has been fixed in version 4.0.19.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-59728 since 07/06/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1055 according to MITRE ATT&CK.

Upgrading to version 4.0.19 eliminates this vulnerability.

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Productinfo

Vendor

• withastro

Name

• astro

Version

• 4.0.0
• 4.0.1
• 4.0.2
• 4.0.3
• 4.0.4
• 4.0.5
• 4.0.6
• 4.0.7
• 4.0.8
• 4.0.9
• 4.0.10
• 4.0.11
• 4.0.12
• 4.0.13
• 4.0.14
• 4.0.15
• 4.0.16
• 4.0.17
• 4.0.18

Website

• Product: https://github.com/withastro/astro/

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