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Critical vulnerability in LangChain – CVE-2025-68664

96 pointsposted 13 hours ago

61 Comments

prodigycorp

11 hours ago

The best part about this is that you know the type of people/companies using langchain are likely the type that are not going to patch this in a timely manner.

peab

7 hours ago

Langchain is great because it provides you an easy method to filter people out when hiring. Candidates who talk about langchain are, more often than not, low quality candidates.

babyshake

6 hours ago

Would you say the same for Mastra? If so, what would you say indicates a high quality candidate when they are discussing agent harnessing and orchestration?

avaer

2 hours ago

I somewhat take issue as a LangChain hater + Mastra lover with 20+ years of coding experience and coding awards to my name (which I don't care about, I only mention it for context).

Langchain is `left-pad` -- a big waste of your time, and Mastra is Next.js -- mostly saving you infrastructure boilerplate if you use it right.

But I think the primary difference is that Python is a very bad language for agent/LLM stuff (e.g. static typesystem, streaming, isomorphic code, strong package management ecosystem is what you want, all of which Python is bad with). And if for some ungodly reason you had to do it in Python, you'd avoid LangChain anyway so you could bolt on strong shim layers to fix Python's shortcomings in a way that won't break when you upgrade packages.

Yes, I know there's LangChain.js. But at that point you might as well use something that isn't a port from Python.

> what would you say indicates a high quality candidate when they are discussing agent harnessing and orchestration?

Anything that shows they understand exactly how data flows through the system (because at some point you're gonna be debugging it). You can even do that with LangChain, but then all you'd be doing is complaining about LangChain.

notnullorvoid

5 hours ago

Curious what your critique is for LangChain?

I found the general premise of the tools (in particular LangGraph) to be solid. I was never in the position to use it (not my current area of work), but had I been I may have suggested building some prototypes with it.

deepsquirrelnet

6 hours ago

It also helps with jobseeking as well. Easy to know which places to avoid.

wilkystyle

11 hours ago

Can you elaborate? Fairly new to langchain, but didn't realize it had any sort of stereotypical type of user.

int_19h

9 hours ago

I'll admit that I haven't looked it in a while, but as originally released, it was a textbook example on how to complicate a fundamentally simple and well-understood task (text templates, basically) with lots of useless abstractions that made it all sound more "enterprise". People would write complicated langchains, but then when you looked under the hood all it was doing is some string concatenation, and the result was actually less readable than a simple template with substitutions in it.

phyzome

2 hours ago

Huh, kind of sounds like they used LLMs to design it. :-)

gcr

8 hours ago

What do you suggest instead? Handrolled code with “import openai”? BAML?

llmslave2

3 hours ago

Oh gosh, not that legacy "hand rolled code"

XCSme

10 hours ago

I am not sure what's the stereotype, but I tried using langchain and realised most of the functionality actually adds more code to use than simply writing my own direct API LLM calls.

Overall I felt like it solves a problem doesn't exist, and I've been happily sending direct API calls for years to LLMs without issues.

teruakohatu

10 hours ago

JSON Structured Output from OpenAI was released a year after the first LangChain release.

I think structured output with schema validation mostly replaces the need for complex prompt frameworks. I do look at the LC source from time to time because they do have good prompts backed into the framework.

avaer

an hour ago

To this day many good models don't support structured outputs (say Opus 4.5) so it's not a panacea you can count on in production.

The bigger problem is that LangChain/Python is the least set up to take advantage of strong schemas even when you do have it.

Agree about pillaging for prompts though.

majormajor

9 hours ago

IME you could get reliable JSON or other easily-parsable output formats out of OpenAI's going back at least to GPT3.5 or 4 in early 2023. I think that was a bit after LangChain's release but I don't recall hitting problems that I needed to add a layer around in order to do "agent"-y things ("dispatch this to this specialized other prompt-plus-chatgpt-api-call, get back structured data, dispatch it to a different specialized prompt-plus-chatgpt-api-call") before it was a buzzword.

nostrebored

5 hours ago

Can guarantee this was not true for any complicated extraction. You could reliably get it to output json but not the json you wanted

Even on smallish ~50k datasets error was still very high and interpretation of schema was not particularly good.

avaer

an hour ago

It's still not true for any complicated extraction. I don't think I've ever shipped a successful solution to anything serious that relied on freeform schema say-and-pray with retries.

Insanity

8 hours ago

When my company organized an LLM hackathon last year, they pushed for LangChain.. but then instead of building on top of it I ended up creating a more lightweight abstraction for our use-cases.

That was more fun than actually using it.

prodigycorp

10 hours ago

No dig at you, but I take the average langchain user as one who is either a) using it because their C-suite heard about at some AI conference and had it foisted upon them or b) does not care about software quality in general.

I've talked to many people who regret building on top of it but they're in too deep.

I think you may come to the same conclusions over time.

inlustra

9 hours ago

Great insight that you wouldn’t get without HN, thank you! What would you and your peers recommend?

baobabKoodaa

9 hours ago

LangChain does not solve any actual problem, so there is no need to replace it with anything. Just build without it.

peab

7 hours ago

There's a great talk called Pydantic is all you need that i highly recommend

sumitkumar

8 hours ago

pydantic/pydanticAI in builder mode or llamaindex in solution architect mode.

wilkystyle

4 hours ago

Thanks for the reply, and no offense taken. I've inherited some code that uses LangChain, and this is my first experience with it.

anonzzzies

9 hours ago

Yep, not sure why anyone is using it still.

blcknight

5 hours ago

What would you use instead?

I built an internal CI chat bot with it like 6 months ago when I was learning. It’s deployed and doing what everyone needs it to do.

Claude Code can do most of what it does without needing anything special. I think that’s the future but I hate the vendor lock in Anthropic is pushing with CC.

All my python tools could be skills, and some folks are doing that now but I don’t need to chase after every shiny thing — otherwise I’d never stop rewriting the damn thing.

Especially since there’s no standardizing yet on plugins/skills/commands/hooks yet.

echelon

7 hours ago

These guys raised $125M at $1.3B post on $12M ARR? What.

> Today, langchain and langgraph have a combined 90M monthly downloads, and 35 percent of the Fortune 500 use our services

What? This seems crazy. Maybe I'm blind, but I don't see the long term billion dollar business op here.

Leftpad also had those stats, iirc.

anonzzzies

7 hours ago

They were the first, very very early in the gpt hype start.

fn-mote

8 hours ago

> The blast radius is scale

Ugh. I’m a native English speaker and this sounds wrong, massaged by LLM or not.

“Large blast radius” would be a good substitute.

I am happy this whole issue doesn’t affect me, so I can stop reading when I don’t like the writing.

morkalork

8 hours ago

Makes you think a human wrote it, which for an article on a .ai domain is kind of shocking!

croemer

8 hours ago

It's definitely LLM generated. I came here to post that, then you saw you had already pointed it out. Giveaway for me: 'The most common real-world path here is not “attacker sends you a serialized blob and you call load().” It’s subtler:'

It's not, it's; bolded items in list.

Also no programmer would use this apostrophe instead of single quote.

minitech

3 hours ago

> Also no programmer would use this apostrophe instead of single quote.

I’m a programmer who likes punctuation, and all of my pointless internet comments are lovingly crafted with Option+]. It’s also the default for some word processors. Probably not wrong about the article, though.

shahartal

13 hours ago

CVE-2025-68664 (langchain-core): object confusion during (de)serialization can leak secrets (and in some cases escalate further). Details and mitigations in the post.

threecheese

11 hours ago

Cheers to all the teams on sev1 calls on their holidays, we can only hope their adversaries are also trying to spend time with family. LangGrinch, indeed! (I get it, timely disclosure is responsible disclosure)

crtasm

8 hours ago

What're the odds they've licenced the Grinch character for use on their company blog?

rainonmoon

6 hours ago

This would make this blog notable as the first AI company to proactively respect trademark.

bad_haircut72

8 hours ago

The vulnerability was that dumps() and dumpd() did not properly escape user-controlled dictionaries that happened to include the reserved ‘lc’ key.

I wonder if this code was written by an LLM hahaha

croemer

8 hours ago

LLM slop. At least one clear error (hallucination): "’Twas the night before Christmas, and I was doing the least festive kind of work: staring at serialization"

Per disclosure timeline the report was made on December 4, it was definitely not the night before Christmas when you were doing the work then.

nextworddev

9 hours ago

Meanwhile Harrison Chase is laughing his way to the bank

nubg

12 hours ago

WHY on earth did the author of the CVE feel the need to feed the description text through an LLm? I get dizzy when I see this AI slop style.

I would rather just read the original prompt that went in instead of verbosified "it's not X, it's **Y**!" slop.

iamacyborg

12 hours ago

> WHY on earth did the author of the CVE feel the need to feed the description text through an LLm?

Not everyone speaks English natively.

Not everyone has taste when it comes to written English.

nkrisc

6 hours ago

I personally find that text written by a human, even someone without a strong grasp of the language, is always preferable to read simply because each word (for better or worse) was chosen by a human to represent their ideas.

If you use an LLM because you think you can’t write and communicate well, then if that’s true it means you’re feeding content that you already believe isn’t worthy of expressing your ideas to a machine that will drag your words even further what you intended.

smj-edison

6 hours ago

Yeah. It feels like the same amount of signal for a larger amount of noise, and I strongly prefer high SNR. Terse and accurate are what I strive for in my writing, so it's painful to read a lot of text only to realize that two sentences would've sufficed.

nubg

11 hours ago

If I want to cleanup, summarize, translate, make more formal, make more funny, whatever, some incoming text by sending it through an LLM, I can do it myself.

crote

10 hours ago

I would rather read succinct English written by a non-native speaker filled with broken grammar than overly verbose but well-spelled AI slop. Heck, just share the prompt itself!

If you can't be bothered to have a human write literally a handful of lines of text, what else can't you be bothered to do? Why should I trust that your CVE even exists at all - let alone is indeed "critical" and worth ruining Christmas over?

llmslave2

3 hours ago

It's actually far more preferable to read broken English written by a human because each language imposes their own unique "flavour" in English making it preferable to AI slop.

iinnPP

10 hours ago

I prefer reading the LLM output for accessibility reasons.

More importantly though, the sheer amount of this complaint on HN has become a great reason not to show up.

crote

9 hours ago

> I prefer reading the LLM output for accessibility reasons.

And that's completely fine! If you prefer to read CVEs that way, nobody is going to stop you from piping all CVE descriptions you're interested in through a LLM.

However, having it processed by a LLM is essentially a one-way operation. If some people prefer the original and some others prefer the LLM output, the obvious move is to share the original with the world and have LLM-preferring readers do the processing on their end. That way everyone is happy with the format they get to read. Sounds like a win-win, no?

iinnPP

9 hours ago

Yes, framed as you stated it is indeed a win-win.

However, there will be cases where lacking the LLM output, there isn't any output at all.

Creating a stigma over technology which is easily observed as being, in some form, accessible is expected in the world we live. As it is on HN.

Not to say you are being any type of anything, I just don't believe anyone has given it all that much thought. I read the complaints and can't distinguish them from someone complaining that they need to make some space for a blind person using their accessibility tools.

crote

8 hours ago

> However, there will be cases where lacking the LLM output, there isn't any output at all.

Why would there be? You're using something to prompt the LLM, aren't you - what's stopping you from sharing the input?

The same logic can be applied in an even larger extent to foreign-language content. I'd 1000x rather have a "My english not good, this describe big LangChain bug, click <link> if want Google Translate" followed by a decent article written in someone's native Chinese, than a poorly-done machine translation output. At least that way I have the option of putting the source text in different translation engines, or perhaps asking a bilingual friend to clarify certain sections. If all you have is the English machine translation output, then you're stuck with that. Something was mistranslated? Good luck reverse engineering the wrong translation back to its original Chinese and then into its proper English equivalent! Anyone who has had the joy to deal with "English" datasheets for Chinese-made chips knows how well this works in practice.

You are definitely bringing up a good point concerning accessibility - but I fear using LLMs for this provides fake accessibility. Just because it results in well-formed sentences doesn't mean you are actually getting something comprehensible out of it! LLMs simply aren't good enough yet to rely on them not losing critical information and not introducing additional nonsense. Until they have reached that point, their user should always verify its output for accuracy - which on the author side means they were - by definition - also able to write it on their own, modulo some irrelevant formatting fluff. If you still want to use it for accessibility, do so on the reader side and make it fully optional: that way the reader is knowingly and willingly accepting its flaws.

The stigma on LLM-generated content exists for a reason: people are getting tired of starting to invest time into reading some article, only for it to become clear halfway through that it is completely meaningless drivel. If >99% of LLM-generated content I come across is an utter waste of my time, why should I give this one the benefit of the doubt? Content written in horribly-broken English at least shows that there is an actual human writer investing time and effort into trying to communicate, instead of it being yet another instance of fully-automated LLM-generated slop trying to DDoS our eyeballs.

MobiusHorizons

2 hours ago

I completely agree I prefer the original language as it offers more choice in how to try to consume it. I believe search engines segment content by source language though, so you would probably not ever see such content in search results for English language queries. It would be cool if you could somehow signal to search engines that you are interested in non-native language results. I don’t even tend to see results in the second language in my accept languages header unless the query is in that language.

llmslave2

3 hours ago

Im sorry but I don't buy the argument that we should be accepting of AI slop because it's more accessible. That type of framing is devious because you frame dissenters as not caring about accessibility. It has nothing to do with accessibility and everything to do with simply not wanting to consume utterly worthless slop.

roywiggins

10 hours ago

Unfortunately, the sheer amount of ChatGPT-processed texts being linked has for me become a reason not to want to read them, which is quite depressing.

colechristensen

9 hours ago

You wouldn't complain as much if it were merely poorly written by a human. It gets the information across. The novelty of complaining about a new style of bad writing is being overdone by a lot of people, particularly on HN.

crote

7 hours ago

> You wouldn't complain as much if it were merely poorly written by a human.

Obviously.

> It gets the information across.

If it is poorly written by a human? Sure!

> The novelty of complaining about a new style of bad writing

But it's not a "new style of bad writing", is it?

The problem is that LLM-generated content is more often than not wrong. It is only worth reading if a human has invested time into post-processing it. However, LLMs make badly-written low-quality content look the same as badly-written high-quality content or decently-written high-quality content. It is impossible for the reader to quickly distinguish properly post-processed LLM output from time-wasting slop.

On the other hand, if its written by a human it is often quite easy to distinguish badly-written low-quality content from badly-written high-quality content. And the writing was never the important part: it has always been about the content. There are plenty of non-native English tech enthusiasts writing absolute gems in the most broken English you can imagine! Nobody has ever had trouble distinguishing those from low-quality garbage.

But the vast majority of LLM-generated content I come across on the internet is slop and a waste of my time. My eyeballs are being DDoSed. The only logical action upon noticing that something is LLM-generated content is to abort reading it and assume it is slop as well. Like it or not, LLMs have become a sign of poor quality.

By extension, the issue with using LLMs for important content is that you are making it look indistinguishable from slop. You are loudly signaling to the reader that it isn't worth their time. So yes, if you want people to read it, stick to bad human writing!