Devalue before 5.9.3 Quadratic Expansion Denial of Service via uneval
- Exploited
- No known exploitation
- Fix
- Fixed in 5.9.3
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Affected devalue versions are those before 5.9.3 Data is parsed and then passed to uneval Only under very constrained circumstances
- Published
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 21/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Sveltejs devalue before 5.9.3 contains a resource exhaustion vulnerability where repeated primitive strings cause quadratic expansion in the uneval function. Attackers can supply a small crafted payload that is parsed and then passed to uneval, producing a very large serialized string that exhausts memory or CPU.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure12/25Specific setups only, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
What to do
Check whether your setup matches what the bug needs.
Affected devalue versions are those before 5.9.3 Data is parsed and then passed to uneval Only under very constrained circumstancesUpgrade to a fixed version: 5.9.3.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- sveltejs devalue
fixed in 5.9.3
Evidence 2
- Advisory
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123565
Is CVE-2026-123565 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
A small crafted payload that is parsed and then passed to uneval can produce a very large serialized string. That can exhaust memory or CPU, which is a denial of service.Source: vulncheck.com, github.com
Which versions are affected by CVE-2026-123565?
devalue: before 5.9.3.Source: cve.now feed data
Am I affected, and how do I check?
Devalue versions before 5.9.3 are affected, and the issue only arises under very constrained circumstances where parsed data is passed to uneval. To check, look at the devalue version in your project's package.json or lockfile and see whether it is below 5.9.3.Source: vulncheck.com, github.com
How do I fix CVE-2026-123565?
Upgrade devalue to 5.9.3 or later, which contains the fix. No workaround is listed in the facts.Source: vulncheck.com, github.com