EUVD-2026-30054
GHSA-xr5h-phrj-8vxv
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/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
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/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
Lifecycle Timeline
4Blast Radius
ecosystem impact- 1 npm packages depend on astro (1 direct, 0 indirect)
Ecosystem-wide dependent count for version 6.1.10.
DescriptionGitHub Advisory
Impact
Astro versions prior to 6.1.10 used AES-GCM encryption to protect the confidentiality and integrity of server island props and slots parameters, but did not bind the ciphertext to its intended component or parameter type. An attacker could replay one component's encrypted props (p) value as another component's slots (s) value, or vice versa.
Since slots contain raw unescaped HTML while props may contain user-controlled values, this could lead to XSS in applications that meet all of the following conditions:
- The application uses server islands
- Two different server island components share the same key name for a prop and a slot
- An attacker has full control over the value of the overlapping prop (requires a dynamically rendered page)
These conditions are very unlikely to occur in real-world production applications.
Patches
This has been patched in astro@6.1.10.
The fix binds each encrypted parameter to its target component and purpose using AES-GCM authenticated additional data (AAD). Each ciphertext now includes context like props:IslandName or slots:IslandName, so encrypted data for one component cannot be replayed against a different component, and encrypted props cannot be reused as slots.
References
- Fix PR: https://github.com/withastro/astro/pull/16457
- Example demonstrating the vulnerability: https://github.com/CyberSecurityAustria/ACSC2026-web-astronomical
AnalysisAI
Astro versions prior to 6.1.10 fail to bind encrypted server island parameters to their intended component and purpose, allowing attackers to replay encrypted props as slots or vice versa. This cryptographic binding failure could lead to cross-site scripting (XSS) when applications use server islands with overlapping prop and slot names where an attacker controls prop values. The vulnerability requires very specific application architecture (shared key names, dynamically rendered pages, attacker-controlled props) making real-world exploitation unlikely, but the underlying encryption design flaw is significant.
Technical ContextAI
Astro's server islands feature uses AES-GCM encryption to protect component props and slots during transmission. The original implementation encrypted these parameters without binding the ciphertext to contextual metadata such as the target component identity or parameter type (props vs. slots). AES-GCM provides both confidentiality and integrity protection, but without authenticated additional data (AAD) binding the ciphertext to its intended use, an attacker can replay encrypted data between different contexts. The vulnerability stems from improper use of AES-GCM; the cipher was present but not fully leveraged for its binding capabilities. The fix adds AAD strings like 'props:ComponentName' or 'slots:ComponentName' to the encryption and decryption operations, ensuring the ciphertext is cryptographically bound to both its component and purpose. This is a CWE-323 (Unprotected Transport of Credentials) variant where the binding mechanism itself was missing.
RemediationAI
Vendor-released patch: Astro 6.1.10 and later. Upgrade immediately by running npm install astro@^6.1.10 or equivalent for your package manager. The fix is non-breaking and applies cryptographic hardening without API changes; no application code modifications are necessary. For environments unable to upgrade immediately, mitigation requires either disabling server islands entirely (set serverIslands: false in astro.config.mjs, though this breaks associated features) or architecturally refactoring to ensure no two different server island components share key names between props and slots (verify by auditing component definitions). The latter is operationally complex and error-prone; immediate patching is strongly recommended. See https://github.com/withastro/astro/security/advisories/GHSA-xr5h-phrj-8vxv and https://github.com/withastro/astro/pull/16457 for advisory details and the complete fix.
Same weakness CWE-323 – Reusing a Nonce, Key Pair in Encryption
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External POC / Exploit Code
Leaving vuln.today