vulnerability / NVI-00010089 / Revision 3
Astro: Arbitrary CSS injection in Astro View Transitions
GitHub lists this reviewed advisory for astro. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
0.498%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.42729. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
astro
source listed>= 7.1.0, <= 7.3.2
### Summary Astro's server-side View Transition CSS generator did not keep string animation properties within their generated CSS declarations. In an application that passes attacker-controlled data into an animation property such as `duration`, a value containing CSS delimiters could terminate the declaration and rule, then add attacker-selected CSS to the server-rendered page. The injected content remains inside the generated `` element. It cannot terminate that element or inject HTML or JavaScript because Astro escapes `<` before emitting the stylesheet. ### Severity Exploitation requires an application to pass untrusted, request-derived, or user-controlled content directly into a transition animation value. This is an uncommon application pattern, and applications using static or otherwise trusted transition values are unaffected. The resulting capability is limited to CSS in the rendered document. The proof of concept does not demonstrate JavaScript execution, HTML injection, an origin-boundary bypass, or access to server-only data. ### Details Animation values are collected by `stringifyAnimations()` in `packages/astro/src/runtime/server/transition.ts` and passe
astro
source listedSEMVER: introduced 7.1.0; fixed 7.3.3
### Summary Astro's server-side View Transition CSS generator did not keep string animation properties within their generated CSS declarations. In an application that passes attacker-controlled data into an animation property such as `duration`, a value containing CSS delimiters could terminate the declaration and rule, then add attacker-selected CSS to the server-rendered page. The injected content remains inside the generated `` element. It cannot terminate that element or inject HTML or JavaScript because Astro escapes `<` before emitting the stylesheet. ### Severity Exploitation requires an application to pass untrusted, request-derived, or user-controlled content directly into a transition animation value. This is an uncommon application pattern, and applications using static or otherwise trusted transition values are unaffected. The resulting capability is limited to CSS in the rendered document. The proof of concept does not demonstrate JavaScript execution, HTML injection, an origin-boundary bypass, or access to server-only data. ### Details Animation values are collected by `stringifyAnimations()` in `packages/astro/src/runtime/server/transition.ts` and passe
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
- vendor patch
The original advisory lists fixed boundaries 7.3.3 for astro. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-mpr7-6m5w-76rw ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- GHSA-mpr7-6m5w-76rw ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
- CVE-2026-114127 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.