CVE-2026-63276: Stack buffer overflow in CFF to Type 1 font conversion
- Is it exploited?
Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of . If CISA adds it, this page shows it as known exploited.
- How likely is exploitation in the next 30 days?
- 0.2%
EPSS score, percentile 9.3 of all scored records. A probability estimated by FIRST, not a report of exploitation.
- How severe?
- 5.4 Medium
CVSS v4.0 base score, given by the CNA
- What should I do?
CISA has set no required action, because the vulnerability is not in KEV.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- from 26.2 to before < 26.2.5
Source: CISA KEV 2026.10.29, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.
What to do
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 26.2 to before < 26.2.5 |
Versions not listed are: unknown.
Source: CVE List, as of . About the data.
About this vulnerability
LibreOffice converts CFF fonts to Type 1 when it subsets a font, which happens when a document is exported to PDF, and CFF fonts may be embedded in documents. A stack buffer overflow existed in that conversion. The converted operators were written into a fixed size buffer with no check that they still fit, so a glyph emitting many operators wrote past the end of the buffer. In fixed versions the…
Summary: CVE record, as of .
- CISA has not added CVE-2026-63276 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
- The CVE record was published on 22 Sep 2026.
- The CVE record carries a CVSS v4.0 base score of 5.4 (Medium), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.2% (percentile 9.3), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
- CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact partial.
- The credits in the CVE record name Anthropic (Claude) as finder.
Source: CISA KEV 2026.10.29, as of ; CVE List, as of ; FIRST EPSS, as of . About the data.
Description
Stack buffer overflow in CFF to Type 1 font conversion
LibreOffice converts CFF fonts to Type 1 when it subsets a font, which happens when a document is exported to PDF, and CFF fonts may be embedded in documents. A stack buffer overflow existed in that conversion. The converted operators were written into a fixed size buffer with no check that they still fit, so a glyph emitting many operators wrote past the end of the buffer. In fixed versions the remaining capacity is tracked and the conversion stops when it is used up.
Source: CVE List, as of . About the data.
Weakness
CWE-787, 1 CAPEC
- CWE-787: Out-of-bounds Write
Attack patterns (CAPEC)
- CAPEC-44: Overflow Binary Resource File
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.
Timeline
| Date | Event |
|---|---|
| CVE record published |