Sveltejs devalue before 5.9.3 Memory Exhaustion via uneval Sparse Arrays
Affects devalue from 1.0.0 before 5.9.3 when very large sparse arrays are serialized with uneval and the output is evaluated. Fixed in 5.9.3.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- 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. Affects devalue from 1.0.0 before 5.9.3 The application serializes very large sparse arrays with uneval and the output is then evaluated
- 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 from 1.0.0 before 5.9.3 contains a memory exhaustion flaw in uneval, whose generated code for sparse arrays allocates memory proportional to the array's declared length when evaluated. Attackers who can influence a very large sparse array serialized by an application can exhaust memory in the browser or runtime evaluating the output.
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.
Affects devalue from 1.0.0 before 5.9.3 The application serializes very large sparse arrays with uneval and the output is then evaluatedUpgrade to a fixed version: 5.9.3.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- sveltejs devalue
From 1.0.0 · 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-2026-123564
Is CVE-2026-123564 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 tiny serialized value can make a consuming browser or runtime allocate a large amount of memory, exhausting it.Source: vulncheck.com, github.com
Which versions are affected by CVE-2026-123564?
devalue: from 1.0.0 before 5.9.3.Source: cve.now feed data
Am I affected, and how do I check?
devalue versions from 1.0.0 before 5.9.3 contain the flaw in uneval. The advisory describes the risky setup as serializing very large sparse arrays with uneval and then evaluating the results. The installed devalue version can be checked in the project's package.json or lockfile.Source: vulncheck.com, github.com
How do I fix CVE-2026-123564?
Upgrade devalue to 5.9.3 or later.Source: vulncheck.com, github.com