fmtlib version prior to version 4.1.0 (before commit 0555cea5fc0bf890afe0071a558e44625a34ba85) contains a Memory corruption (SIGSEGV), CWE-1
fmtlib version prior to version 4.1.0 (before commit 0555cea5fc0bf890afe0071a558e44625a34ba85) contains a Memory corruption (SIGSEGV), CWE-134 vulnerability in fmt::print() library function that can result in Denial of Service. This attack appear to be exploitable via Specifying an invalid format specifier in the fmt::print() function results in a SIGSEGV (memory corruption, invalid write). This vulnerability appears to have been fixed in after commit 8cf30aa2be256eba07bb1cefb998c52326e846e7.
- Published
- Feb 9, 2018
- Updated
- Jun 16, 2026
- EPSS
- 1.4% · 70th percentile
- CWE
- CWE-134
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Report tools
Action score
30
Monitor
Low priority for now.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 1.4%
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| fmt | fmt | cpe:2.3:a:fmt:fmt |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- fmt fmtbefore 4.1.0
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | fmtlib | before 5.2.1+ds-1 | 5.2.1+ds-1 |
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| debian:fmtlib | 5.2.1+ds-1 · Debian:12 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- none
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- None
- Availability impact
- High
Weakness class (CWE)
CWE-134 · Use of Externally-Controlled Format StringCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
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Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.