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RUSTSEC-2026-0194
No affected components available
BytesStart::attributes() returns an Attributes iterator which, by default
(with_checks(true)), rejects a start tag that repeats an attribute name. For
each attribute yielded, the iterator compared the new name against every name
seen so far in the same tag using a linear scan, so a start tag with N
distinct attribute names cost O(N²) byte comparisons. There was no bound on
N other than the size of the buffered start tag.
Impact
Any code that parses untrusted XML and iterates a start tag's attributes with
the default duplicate check enabled can be made to spend CPU time quadratic in
the number of attributes on a single tag. Because the check is pure computation
with no .await/I/O, an I/O-based timeout on the consumer (for example a read
or request timeout) cannot interrupt it while it runs.
Measured cost of a single start tag, release build:
| Attributes on one tag | Time | |---|---| | 80,000 | ~6 s | | 800,000 | ~10 min |
The cost grows with the square of the attribute count, so a start tag of a few tens of megabytes can stall a parsing thread for hours. No memory is exhausted and the parser does not crash; the effect is CPU exhaustion on the thread doing the parsing: a single crafted start tag can pin a CPU core for minutes to hours, denying service to that worker. A deployment that places a wall-clock bound on parsing, or confines it to a non-critical thread, may consider the availability impact lower.
Affected code paths
BytesStart::attributes()/Attributesiterated with checks enabled (the default), andBytesStart::try_get_attribute.NsReader, which resolves namespaces by iterating a tag's attributes and so reaches the same check internally.
Consumers that iterate attributes with .attributes().with_checks(false) and do
not use NsReader are not affected.
This was reported as reachable by a remote, unauthenticated attacker in a
real-world RPKI relying party (NLnet Labs Routinator) via a crafted RRDP
snapshot.xml.
Remediation
Upgrade to quick-xml >= 0.41.0, where the duplicate check keeps the linear
scan for start tags with a small number of attributes and switches to an O(1)
hash pre-filter above a threshold, making the whole tag O(N). The reported
AttrError::Duplicated positions are unchanged.
If upgrading is not possible and duplicate-name detection is not required,
disable it with .attributes().with_checks(false) (this does not help
NsReader consumers, which have no equivalent opt-out before 0.41.0).
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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