parse-server: Stored XSS via trailing-dot filename bypassing file upload extension blocklist
Exact source revision recorded 24 Oct 2026 13:17:17 UTC. It does not establish the source's current position. Latest evidence.
osv · GHSA-7wqv-xjf3-x35v
Published### Impact The default file upload extension blocklist can be bypassed by appending a trailing dot to a filename whose extension would otherwise be blocked (e.g. `poc.svg.`). The trailing dot causes the extension parser to extract an empty string, which short-circuits the blocklist check, and the attacker-controlled Content-Type is forwarded to the storage adapter unchanged. Storage adapters that persist and serve the provided Content-Type (such as S3 or GCS) then serve the file with an active type such as `image/svg+xml`, enabling stored XSS when a victim opens the file URL. The default GridFS adapter is not affected because it sets `X-Content-Type-Options: nosniff` on responses. ### Patches A filename ending in a dot is now treated as extensionless. When the parser produces an empty extension, the request handler falls back to validating the Content-Type subtype against the configured extension blocklist, matching the path that already catches truly extensionless uploads with a dangerous Content-Type. This is a follow-up to the previous fix [GHSA-vr5f-2r24-w5hc](https://github.com/parse-community/parse-server/security/advisories/GHSA-vr5f-2r24-w5hc). ### Workarounds Configure the storage adapter or CDN to derive Content-Type from the filename extension instead of using the stored Content-Type, or replace the default blocklist with an explicit allowlist of needed file extensions.
- Source published
- 19 Jun 2026 19:35:11 UTC
- Source modified
- 19 Jun 2026 19:56:23 UTC
- Observed here
- 24 Oct 2026 13:17:17 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
Publisher rating · LOW