tls: fix handling of zero-length records on the rx_list
Published · Updated
78Vexday Risk Score
Prioritize patching. It under exploitation confirmed by CISA and has a public proof of concept.
ssvc Actcvss 9.8epss 2.9%
from disclosure to weapon39 days
Published on NVDSep 5
1st PoC+39d
CISA KEV+378d
exploitation probability
2.9%top 14% of all CVEs
observed exploitation
yesCISA + VulnCheck
1 public exploit(s)
Action required by CISAfederal deadline: 2026-09-21
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
In short
The Linux kernel's TLS implementation fails to properly handle zero-length records that come from an internal queue (rx_list), potentially causing memory corruption or denial of service. This flaw affects systems using TLS encryption, particularly with TLS 1.3 where record types are only known after decryption.
Technical detail
A zero-length TLS record retrieved from the rx_list after zero-copy decryption can bypass proper state validation, as the kernel assumes zero-copy operations only occur with data records. An attacker able to influence TLS record processing (network-level or via malicious TLS server) can trigger this path, potentially leading to memory safety violations or crashes in the kernel's TLS stack.
Summary generated and translated by AI from the official description.
In the Linux kernel, the following vulnerability has been resolved:
tls: fix handling of zero-length records on the rx_list
Each recvmsg() call must process either
- only contiguous DATA records (any number of them)
- one non-DATA record
If the next record has different type than what has already been
processed we break out of the main processing loop. If the record
has already been decrypted (which may be the case for TLS 1.3 where
we don't know type until decryption) we queue the pending record
to the rx_list. Next recvmsg() will pick it up from there.
Queuing the skb to rx_list after zero-copy decrypt is not possible,
since in that case we decrypted directly to the user space buffer,
and we don't have an skb to queue (darg.skb points to the ciphertext
skb for access to metadata like length).
Only data records are allowed zero-copy, and we break the processing
loop after each non-data record. So we should never zero-copy and
then find out that the record type has changed. The corner case
we missed is when the initial record comes from rx_list, and it's
zero length.