In the Linux kernel, the following vulnerability has been resolved:
netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets
Commit be0502a3f2e9 ("netfilter: conntrack: tcp: only close if RST
matches exact sequence") keeps an established conntrack entry in
ESTABLISHED when an in-window RST does not match the expected sequence
number exactly, so the endpoint can validate the RST with a challenge
ACK.
The timeout selection nevertheless uses the CLOSE timeout for every RST
packet. The bug is that timeout selection is based on the packet type,
not on the state transition result: even when RST validation keeps
new_state in ESTABLISHED, the timeout is still forced to
TCP_CONNTRACK_CLOSE.
Linux TCP independently rate limits challenge ACKs per socket. A second
non-exact RST can therefore arrive after the first challenge ACK has
restored the timeout but before the rate limit expires. The second RST
lowers the timeout to 10 seconds again while the endpoint suppresses the
second challenge ACK, allowing the conntrack entry to expire while both
TCP endpoints remain established.
Using the ESTABLISHED timeout for such RSTs would avoid this short
expiration window, but it could also retain stale entries for the
five-day default because conntrack cannot reliably match the endpoint's
exact TCP state.
Use the UNACK timeout for RST packets that leave the conntrack entry in
TCP_CONNTRACK_ESTABLISHED. Exact-match RSTs and accepted RST packet
trains still fall through to timeouts[new_state], which preserves the
CLOSE timeout when conntrack accepts the RST as closing the flow.
This avoids the aggressive 10-second expiration window for non-exact
RSTs while preserving the short timeout for RSTs that conntrack accepts
as closing the flow.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
- EG Severity
- Not assessed: no CVSS publishedA missing CVSS is not a severity of zero.
- EG Likelihood
- Unknown (no EPSS on record)Unknown, not low: FIRST has published no EPSS probability for this CVE.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- No SSVC decision: EchelonGraph has not assessed this CVECISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.Each input and its source, and whom BOD 26-04 binds: the BOD 26-04 block below.
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it