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CVE-2026-82259

SvelteKit 2.49.0 before 2.53.3 Denial of Service via form

8.7 HighFix available

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

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
High

Exploit likelihood

0.53%Up 0.2 points since Aug 29, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.7

SvelteKit 2.49.0 before 2.53.3 Denial of Service via form

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

Record
CVE-2026-82259
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-502
Updated
2026-11-02
EUVDEUVD-2026-67585 8.7

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

Record
EUVD-2026-67585
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-7jhg-723h-fjhx 8.7

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization...

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

Record
GHSA-7jhg-723h-fjhx
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/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
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-502
Updated
2026-11-02
GitHub AdvisoriesGHSA-fpg4-jhqr-589c 1.7

SvelteKit has deserialization expansion in unvalidated `form` remote function leading to Denial of Service (experimental only)

Some relatively small inputs can cause very large files arrays in form handlers. If the SvelteKit application code doesn't check files.length or individual files' sizes and performs expensive processing with them, it can result in Denial of Service.

Only users with experimental.remoteFunctions: true who are using the form function and are processing the files array without validation are vulnerable.

Record
GHSA-fpg4-jhqr-589c
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U
Weakness
CWE-770
Updated
2026-11-02
NVD 8.7

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

Record
CVE-2026-82259
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/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
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-502
Updated
2026-11-02
OSV 8.7

SvelteKit 2.49.0 before 2.53.3 Denial of Service via form

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

Record
CVE-2026-82259
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-502
Updated
2026-11-02
OSVGHSA-fpg4-jhqr-589c 1.7

SvelteKit has deserialization expansion in unvalidated `form` remote function leading to Denial of Service (experimental only)

Some relatively small inputs can cause very large files arrays in form handlers. If the SvelteKit application code doesn't check files.length or individual files' sizes and performs expensive processing with them, it can result in Denial of Service.

Only users with experimental.remoteFunctions: true who are using the form function and are processing the files array without validation are vulnerable.

Record
GHSA-fpg4-jhqr-589c
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U
Weakness
CWE-770
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
@sveltejs/kit
npm
2.49.0 to 2.53.2
2.53.3
@sveltejs/kit
npm
2.49.0 up to 2.53.3
2.53.3

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-82259 is a high vulnerability (CVSS 8.7) in Svelte Sveltekit, published February 28, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.53%, the 45th percentile. Fixed in @sveltejs/kit 2.53.3.

References

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