CVE-2026-6691: mongodb inc mongodb c driver Classic Buffer Overflow
CVSS: 8.6v4.0HighAnalyzed
AliasesUBUNTU-CVE-2026-6691DEBIAN-CVE-2026-6691
Published 06-05-2026Last modified 07-05-2026
Vulnerability summary
CVE-2026-6691 is a high (CVSS 8.6) Classic Buffer Overflow vulnerability in mongodb inc mongodb c driver. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 7.5% of scored vulnerabilities.
CVSS score
8.6/10
010
High · v4.0 (CVE.org)EPSS score
0.18%
0%100%
Low · +0.06 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Timeline
- 06-05-2026PublishedVulnerability first disclosed.
- 07-05-2026Last modifiedVulnerability information updated.
Description
The MongoDB C Driver's Cyrus SASL integration performs unsafe string copying during username canonicalization, enabling a heap buffer overflow before any authentication or network traffic. This may be triggered by passing untrusted input in the username of a MongoDB URI with authMechanism=GSSAPI.
CVSS metrics
7 scores · 4 sources · 2 versionsHigh 8.6Preferred score · CVE.org (CNA)
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:NSourcesAll 4 agree
- OSV · UbuntuEcosystem advisory · calculated8.6HighCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · DebianEcosystem advisory · calculated8.6HighCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- NVDNIST8.6HighCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
High 7.8Preferred score · CVE.org (CNA)
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HSourcesAll 3 agree
- OSV · UbuntuEcosystem advisory · calculated7.8HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- NVDNIST7.8HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.18%
Chance of exploitation in the next 30 days
Percentile
8%
Versus all other CVEs
30-day change
+0.06 pp
From 0.13% on 19-09-2026
19-09-202619-10-2026
EPSS score0.18%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
- CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.
Affected systems
Debian1 product
- mongo-c-driver< 1.23.1-1+deb12u3 | < 1.30.4-1+deb13u2 | < 2.2.0-1
Mongodb1 product
- c_driver≥ 2.1.0, < 2.1.2
Mongodb inc1 product
- mongodb c driver≥ 2.1.0, ≤ 2.1.2
Ubuntu1 product
- mongo-c-driverAll versions (No fix recorded)
4 vendors · 4 products
