CVE-2026-50290 @asymmetric-effort/specifyjs: CSS expression sanitization is bypassable in renderToString
Attacker can bypass CSS sanitization to inject malicious scripts in legacy browsers, requiring an upgrade to the SpecifyJS library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-50290?
CVE-2026-50290 is a medium-severity cross-site scripting vulnerability in asymmetric-effort specifyjs, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
SpecifyJS is a declarative TypeScript user interface framework. Prior to version 0.2.136, CSS value sanitization stripped `expression(` and `url(javascript:` using simple regex, but could be bypassed with CSS unicode escapes (`\65xpression(`), null bytes, or CSS comments (`exp/**/ression(`). These CSS injection vectors only work in legacy browsers (IE6-IE10). SpecifyJS targets modern browsers. Starting in version 0.2.136, CSS sanitization now normalizes unicode escapes and strips CSS comments before pattern matching. Also checks for `behavior:`, `-moz-binding`, and `-o-link` patterns.
Weakness: CWE-79
Which versions are affected by CVE-2026-50290?
2 open source packages ship an affected version, including @asymmetric-effort/specifyjs.
| Package | Affected | Fixed in |
|---|---|---|
@asymmetric-effort/specifyjs npm | All versions | 0.2.136 |
@asymmetric-effort/specifyjs npm | All versions | 0.2.136 |
How do I fix CVE-2026-50290?
Upgrade @asymmetric-effort/specifyjs to 0.2.136 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-50290 being exploited?
There is no known exploitation of CVE-2026-50290 in the wild and no public exploit code.
Sources
Also known as GHSA-93q6-wwjh-jc6h.