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CVE-2026-64208
crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks
Published 2026-07-24 (3 months ago) by the Linux kernel CNA. Subsystem Documentation/crypto. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64208 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Change the krb5 crypto library to provide facilities to precheck the length of the message about to be decrypted or verified. Fix AF_RXRPC to make use of this to validate DATA packets secured with RxGK.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
Documentation/crypto/krb5.rst
crypto/krb5/krb5_api.c
include/crypto/krb5.h
include/trace/events/rxrpc.h
net/rxrpc/rxgk.c
- What this is
- CRYPTO APIMAINTAINERS section matched on Documentation/crypto/ · linux-crypto@vger.kernel.org · Maintained
- Kernel module
- krb5
Check it on the machine
grep -w CONFIG_CRYPTO_KRB5 /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w krb5Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release with an answer below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidm
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_CRYPTO_KRB5
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-24 (3 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.61%, higher than 48.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- Documentation/crypto
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.34 | 585f9f6aef5c |
| 6.16 | 7.0.11 | 9217017f4bce |
| 6.16 | 7.1 | 2b50aceafe66 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- Attacker-controlled RxRPC DATA packets reach the vulnerable RxGK verifier over UDP. A malicious contacted server can exercise the client receive path without network proximity.
- AC:LAttack complexity, low
- A single deliberately short packet triggers the faulty length handling without a race or uncontrollable condition. Visible RxRPC header fields allow the peer to target an active call reliably.
- PR:NPrivileges required, none
- The length handling occurs before MIC verification or decryption authenticates the packet. A malicious RxRPC server therefore needs no valid Kerberos key or credentials.
- UI:NUser interaction, none
- No human action is required once an application or mounted AFS/YFS client communicates over the RxGK connection. Packet processing and call termination occur automatically.
- S:UScope, unchanged
- The vulnerable RxRPC processing and resulting impact remain within the host kernel's security authority. No VM, sandbox, or IOMMU boundary is crossed.
- C:NConfidentiality impact, none
- The underlying Kerberos implementations reject blobs shorter than their cryptographic overhead before accessing packet data. No out-of-bounds read or information disclosure is supported by the affected path.
- I:NIntegrity impact, none
- The malformed length does not produce an out-of-bounds write or attacker-controlled modification. Existing post-decryption checks prevent reading or applying a truncated inner header.
- A:HAvailability impact, high
- A short unauthenticated packet aborts the active RxRPC call, and repeated injections can continuously deny RxGK-protected AFS/YFS operations. This can make a critical network filesystem or dependent service unavailable.