CVE-2026-84969 Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output
Heap overflow in MongoDB C Driver allows attackers to corrupt memory via truncated base64 encoding, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84969?
CVE-2026-84969 is a medium-severity memory corruption vulnerability in MongoDB C Driver, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A memory-handling error in the BSON-to-JSON conversion helpers of the MongoDB C Driver can write a small number of bytes past the end of a heap buffer when a binary field is encoded and the output is cut short at a caller-configured length limit. A party who supplies the document content, with no privileges on the application that links the driver, may cause a small amount of data outside the intended buffer to be altered.
Weakness: CWE-787
Which versions are affected by CVE-2026-84969?
It affects 1 product.
Products include Mongodb C Driver.
How do I fix CVE-2026-84969?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-84969 being exploited?
There is no known exploitation of CVE-2026-84969 in the wild and no public exploit code.
Other vulnerabilities in MongoDB C Driver
- CVE-2026-93393 Heap overflow via oversized decrypted TLS record sequence in Windows Secure Channel stream
- CVE-2026-6691 MongoDB C Driver Cyrus SASL Canonicalization Buffer Overflow
- CVE-2026-84964 Heap corruption via OCSP request double free from crafted multi-URL certificate in TLS client
- CVE-2024-7553 Accessing Untrusted Directory May Allow Local Privilege Escalation
- CVE-2026-93395 Integer Underflow → Heap Out-of-Bounds Read in `bson_new_from_buffer()
Sources
Also known as DEBIAN-CVE-2026-84969, GHSA-9xr7-hhfx-wh4c, UBUNTU-CVE-2026-84969.