CVE-2026-66062
SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
- Record
CVE-2026-66062- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-1333
- Updated
- 2026-11-02
EUVDEUVD-2026-54557
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
- Record
EUVD-2026-54557- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-29g2-3rmr-qm68
SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
Impact
SvelteKit is vulnerable to remote CPU-exhaustion DoS attacks via specifically-crafted Accept headers. The impact is mitigated by default header length limits on most platforms, but in the case of raised or absent limits a denial of service is possible.
Patches
The vulnerability is patched in @sveltejs/kit version 2.70.2.
- Record
GHSA-29g2-3rmr-qm68- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-1333
- Updated
- 2026-11-02
NVD
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
- Record
CVE-2026-66062- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-1333
- Updated
- 2026-11-02
OSV
SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
- Record
CVE-2026-66062- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-1333
- Updated
- 2026-11-02
OSVGHSA-29g2-3rmr-qm68
SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
Impact
SvelteKit is vulnerable to remote CPU-exhaustion DoS attacks via specifically-crafted Accept headers. The impact is mitigated by default header length limits on most platforms, but in the case of raised or absent limits a denial of service is possible.
Patches
The vulnerability is patched in @sveltejs/kit version 2.70.2.
- Record
GHSA-29g2-3rmr-qm68- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-1333
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
@sveltejs/kitnpm |
through 2.70.1 | 2.70.2 |
@sveltejs/kitnpm |
before 2.70.2 | 2.70.2 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-66062 is a medium vulnerability (CVSS 5.3) in Sveltejs Kit, published August 7, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.51%, the 43rd percentile. Fixed in @sveltejs/kit 2.70.2.
References
github.com/sveltejs/kit/security/advisories/GHSA-29g2-3rmr-qm68
nvd.nist.gov/vuln/detail/CVE-2026-66062