CVE-2026-29795 is a medium-severity (CVSS 4) CWE-770 vulnerability in stellar-xdr. A fix is available for stellar-xdr — see the affected versions and patch details below.
stellar-xdr: `StringM::from_str` bypasses max length validation
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-29795.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-29795 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
stellar-xdrReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Impact
StringM::from_str does not validate that the input length is within the declared maximum (MAX). Calling StringM::<N>::from_str(s) where s is longer than N bytes succeeds and returns an Ok value instead of Err(Error::LengthExceedsMax), producing a StringM that violates its length invariant.
This affects any code that constructs StringM values from string input using FromStr (including str::parse), and relies on the type's maximum length constraint being enforced. An oversized StringM could propagate through serialization, validation, or other logic that assumes the invariant holds.
All published versions of the stellar-xdr crate up to and including v25.0.0 are affected.
Patches
The fix is merged in #500. It replaces the direct Ok(Self(b)) construction with b.try_into(), which routes through TryFrom<Vec<u8>> and properly validates the length — matching the pattern already used by BytesM::from_str.
Users should upgrade to the first release containing this fix once published (the next release after v25.0.0).
Workarounds
Validate the byte length of string input before calling StringM::from_str, or construct StringM values via StringM::try_from(s.as_bytes().to_vec()) which correctly enforces the length constraint.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | stellar-xdr | all versions | 25.0.1cargo update -p stellar-xdr --precise 25.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for stellar-xdr, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update stellar-xdr to 25.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29795 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-29795 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-29795. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-29795 in your dependencies?
O3 Security finds CVE-2026-29795 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.